Beef up travis CI integration testing

Introduces gen_travis.py, which generates .travis.yml, and updates .travis.yml
to be the generated version.

The travis build matrix approach doesn't play well with mixing and matching
various different environment settings, so we generate every build explicitly,
rather than letting them do it for us.

To avoid abusing travis resources (and save us time waiting for CI results), we
don't test every possible combination of options; we only check up to 2 unusual
settings at a time.

scripts/gen_travis.py

@@ -0,0 +1,86 @@
+#!/usr/bin/env python
+
+from itertools import combinations
+
+travis_template = """\
+language: generic
+
+matrix:
+  include:
+%s
+
+before_script:
+  - autoconf
+  - ./configure ${COMPILER_FLAGS:+ \
+      CC="$CC $COMPILER_FLAGS" \
+      CXX="$CXX $COMPILER_FLAGS" } \
+      $CONFIGURE_FLAGS
+  - make -j3
+  - make -j3 tests
+
+script:
+  - make check
+"""
+
+# The 'default' configuration is gcc, on linux, with no compiler or configure
+# flags.  We also test with clang, -m32, --enable-debug, --enable-prof,
+# --disable-stats, and --disable-tcache.  To avoid abusing travis though, we
+# don't test all 2**7 = 128 possible combinations of these; instead, we only
+# test combinations of up to 2 'unusual' settings, under the hope that bugs
+# involving interactions of such settings are rare.
+# things at once, for C(7, 0) + C(7, 1) + C(7, 2) = 29
+MAX_UNUSUAL_OPTIONS = 2
+
+os_default = 'linux'
+os_unusual = 'osx'
+
+compilers_default = 'CC=gcc CXX=g++'
+compilers_unusual = 'CC=clang CXX=clang++'
+
+compiler_flag_unusuals = ['-m32']
+
+configure_flag_unusuals = [
+    '--enable-debug', '--enable-prof', '--disable-stats', '--disable-tcache',
+]
+
+all_unusuals = (
+    [os_unusual] + [compilers_unusual] + compiler_flag_unusuals
+    + configure_flag_unusuals
+)
+
+unusual_combinations_to_test = []
+for i in xrange(MAX_UNUSUAL_OPTIONS + 1):
+    unusual_combinations_to_test += combinations(all_unusuals, i)
+
+include_rows = ""
+for unusual_combination in unusual_combinations_to_test:
+    os = os_default
+    if os_unusual in unusual_combination:
+        os = os_unusual
+
+    compilers = compilers_default
+    if compilers_unusual in unusual_combination:
+        compilers = compilers_unusual
+
+    compiler_flags = [
+        x for x in unusual_combination if x in compiler_flag_unusuals]
+
+    configure_flags = [
+        x for x in unusual_combination if x in configure_flag_unusuals]
+
+    # Filter out an unsupported configuration - heap profiling on OS X.
+    if os == 'osx' and '--enable-prof' in configure_flags:
+        continue
+
+    env_string = '{} COMPILER_FLAGS="{}" CONFIGURE_FLAGS="{}"'.format(
+        compilers, " ".join(compiler_flags), " ".join(configure_flags))
+
+    include_rows += '    - os: %s\n' % os
+    include_rows += '      env: %s\n' % env_string
+    if '-m32' in unusual_combination and os == 'linux':
+        include_rows += '      addons:\n'
+	include_rows += '        apt:\n'
+	include_rows += '          packages:\n'
+	include_rows += '            - gcc-multilib\n'
+
+print travis_template % include_rows