Implement Valgrind support, redzones, and quarantine.

Implement Valgrind support, as well as the redzone and quarantine
features, which help Valgrind detect memory errors.  Redzones are only
implemented for small objects because the changes necessary to support
redzones around large and huge objects are complicated by in-place
reallocation, to the point that it isn't clear that the maintenance
burden is worth the incremental improvement to Valgrind support.

Merge arena_salloc() and arena_salloc_demote().

Refactor i[v]salloc() to expose the 'demote' option.

doc/jemalloc.xml.in

@@ -720,6 +720,16 @@ for (i = 0; i < nbins; i++) {
         build configuration.</para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term>
+          <mallctl>config.valgrind</mallctl>
+          (<type>bool</type>)
+          <literal>r-</literal>
+        </term>
+        <listitem><para><option>--enable-valgrind</option> was specified during
+        build configuration.</para></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term>
           <mallctl>config.xmalloc</mallctl>
@@ -819,6 +829,47 @@ for (i = 0; i < nbins; i++) {
         configuration, in which case it is enabled by default.</para></listitem>
       </varlistentry>
 
+      <varlistentry id="opt.quarantine">
+        <term>
+          <mallctl>opt.quarantine</mallctl>
+          (<type>size_t</type>)
+          <literal>r-</literal>
+          [<option>--enable-fill</option>]
+        </term>
+        <listitem><para>Per thread quarantine size in bytes.  If non-zero, each
+        thread maintains a FIFO object quarantine that stores up to the
+        specified number of bytes of memory.  The quarantined memory is not
+        freed until it is released from quarantine, though it is immediately
+        junk-filled if the <link
+        linkend="opt.junk"><mallctl>opt.junk</mallctl></link> option is
+        enabled.  This feature is of particular use in combination with <ulink
+        url="http://http://valgrind.org/">Valgrind</ulink>, which can detect
+        attempts to access quarantined objects.  This is intended for debugging
+        and will impact performance negatively.  The default quarantine size is
+        0.</para></listitem>
+      </varlistentry>
+
+      <varlistentry id="opt.redzone">
+        <term>
+          <mallctl>opt.redzone</mallctl>
+          (<type>bool</type>)
+          <literal>r-</literal>
+          [<option>--enable-fill</option>]
+        </term>
+        <listitem><para>Redzones enabled/disabled.  If enabled, small
+        allocations have redzones before and after them.  Furthermore, if the
+        <link linkend="opt.junk"><mallctl>opt.junk</mallctl></link> option is
+        enabled, the redzones are checked for corruption during deallocation.
+        However, the primary intended purpose of this feature is to be used in
+        combination with <ulink
+        url="http://http://valgrind.org/">Valgrind</ulink>, which needs
+        redzones in order to do effective buffer overflow/underflow detection.
+        This option is intended for debugging and will impact performance
+        negatively.  This option is disabled by default unless
+        <option>--enable-debug</option> is specified during configuration, in
+        which case it is enabled by default.</para></listitem>
+      </varlistentry>
+
       <varlistentry id="opt.zero">
         <term>
           <mallctl>opt.zero</mallctl>
@@ -849,6 +900,25 @@ for (i = 0; i < nbins; i++) {
         is disabled by default.</para></listitem>
       </varlistentry>
 
+      <varlistentry id="opt.valgrind">
+        <term>
+          <mallctl>opt.valgrind</mallctl>
+          (<type>bool</type>)
+          <literal>r-</literal>
+          [<option>--enable-valgrind</option>]
+        </term>
+        <listitem><para><ulink
+        url="http://http://valgrind.org/">Valgrind</ulink> support
+        enabled/disabled.  If enabled, several other options are automatically
+        modified during options processing to work well with Valgrind: <link
+        linkend="opt.junk"><mallctl>opt.junk</mallctl></link> and <link
+        linkend="opt.zero"><mallctl>opt.zero</mallctl></link> are set to false,
+        <link linkend="opt.quarantine"><mallctl>opt.quarantine</mallctl></link>
+        is set to 16 MiB, and <link
+        linkend="opt.redzone"><mallctl>opt.redzone</mallctl></link> is set to
+        true.  This option is disabled by default.</para></listitem>
+      </varlistentry>
+
       <varlistentry id="opt.xmalloc">
         <term>
           <mallctl>opt.xmalloc</mallctl>
@@ -1764,10 +1834,11 @@ malloc_conf = "xmalloc:true";]]></programlisting>
 
     <para>This implementation does not provide much detail about the problems
     it detects, because the performance impact for storing such information
-    would be prohibitive.  There are a number of allocator implementations
-    available on the Internet which focus on detecting and pinpointing problems
-    by trading performance for extra sanity checks and detailed
-    diagnostics.</para>
+    would be prohibitive.  However, jemalloc does integrate with the most
+    excellent <ulink url="http://http://valgrind.org/">Valgrind</ulink> tool if
+    the <option>--enable-valgrind</option> configuration option is enabled and
+    the <link linkend="opt.valgrind"><mallctl>opt.valgrind</mallctl></link>
+    option is enabled.</para>
   </refsect1>
   <refsect1 id="diagnostic_messages">
     <title>DIAGNOSTIC MESSAGES</title>