Add --with-version.

Also avoid deleting the VERSION file while trying to (re)generate it.

This resolves #305.

INSTALL

@@ -35,6 +35,10 @@ any of the following arguments (not a definitive list) to 'configure':
     will cause files to be installed into /usr/local/include, /usr/local/lib,
     and /usr/local/man.
 
+--with-version=<major>.<minor>.<bugfix>-<nrev>-g<gid>
+    Use the specified version string rather than trying to generate one (if in
+    a git repository) or use existing the VERSION file (if present).
+
 --with-rpath=<colon-separated-rpath>
     Embed one or more library paths, so that libjemalloc can find the libraries
     it is linked to.  This works only on ELF-based systems.

configure.ac

@@ -1172,27 +1172,36 @@ dnl ============================================================================
 dnl jemalloc configuration.
 dnl 
 
-dnl Set VERSION if source directory is inside a git repository.
+AC_ARG_WITH([version],
-if test "x`test ! \"${srcroot}\" && cd \"${srcroot}\"; git rev-parse --is-inside-work-tree 2>/dev/null`" = "xtrue" ; then
+  [AS_HELP_STRING([--with-version=<major>.<minor>.<bugfix>-<nrev>-g<gid>],
-  dnl Pattern globs aren't powerful enough to match both single- and
+   [Version string])],
-  dnl double-digit version numbers, so iterate over patterns to support up to
+  [
-  dnl version 99.99.99 without any accidental matches.
+    echo "${with_version}" | grep ['^[0-9]\+\.[0-9]\+\.[0-9]\+-[0-9]\+-g[0-9a-f]\+$'] 2>&1 1>/dev/null
-  rm -f "${objroot}VERSION"
+    if test $? -ne 0 ; then
-  for pattern in ['[0-9].[0-9].[0-9]' '[0-9].[0-9].[0-9][0-9]' \
+      AC_MSG_ERROR([${with_version} does not match <major>.<minor>.<bugfix>-<nrev>-g<gid>])
-                 '[0-9].[0-9][0-9].[0-9]' '[0-9].[0-9][0-9].[0-9][0-9]' \
-                 '[0-9][0-9].[0-9].[0-9]' '[0-9][0-9].[0-9].[0-9][0-9]' \
-                 '[0-9][0-9].[0-9][0-9].[0-9]' \
-                 '[0-9][0-9].[0-9][0-9].[0-9][0-9]']; do
-    if test ! -e "${objroot}VERSION" ; then
-      (test ! "${srcroot}" && cd "${srcroot}"; git describe --long --abbrev=40 --match="${pattern}") > "${objroot}VERSION.tmp" 2>/dev/null
-      if test $? -eq 0 ; then
-        mv "${objroot}VERSION.tmp" "${objroot}VERSION"
-        break
-      fi
     fi
-  done
+    echo "$with_version" > "${objroot}VERSION"
-fi
+  ], [
-rm -f "${objroot}VERSION.tmp"
+    dnl Set VERSION if source directory is inside a git repository.
+    if test "x`test ! \"${srcroot}\" && cd \"${srcroot}\"; git rev-parse --is-inside-work-tree 2>/dev/null`" = "xtrue" ; then
+      dnl Pattern globs aren't powerful enough to match both single- and
+      dnl double-digit version numbers, so iterate over patterns to support up
+      dnl to version 99.99.99 without any accidental matches.
+      for pattern in ['[0-9].[0-9].[0-9]' '[0-9].[0-9].[0-9][0-9]' \
+                     '[0-9].[0-9][0-9].[0-9]' '[0-9].[0-9][0-9].[0-9][0-9]' \
+                     '[0-9][0-9].[0-9].[0-9]' '[0-9][0-9].[0-9].[0-9][0-9]' \
+                     '[0-9][0-9].[0-9][0-9].[0-9]' \
+                     '[0-9][0-9].[0-9][0-9].[0-9][0-9]']; do
+        (test ! "${srcroot}" && cd "${srcroot}"; git describe --long --abbrev=40 --match="${pattern}") > "${objroot}VERSION.tmp" 2>/dev/null
+        if test $? -eq 0 ; then
+          mv "${objroot}VERSION.tmp" "${objroot}VERSION"
+          break
+        fi
+      done
+    fi
+    rm -f "${objroot}VERSION.tmp"
+  ])
+
 if test ! -e "${objroot}VERSION" ; then
   if test ! -e "${srcroot}VERSION" ; then
     AC_MSG_RESULT(