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.

configure.ac

@@ -685,7 +685,8 @@ AC_SUBST([enable_dss])
 
 dnl Support the junk/zero filling option by default.
 AC_ARG_ENABLE([fill],
-  [AS_HELP_STRING([--disable-fill], [Disable support for junk/zero filling])],
+  [AS_HELP_STRING([--disable-fill],
+                  [Disable support for junk/zero filling, quarantine, and redzones])],
 [if test "x$enable_fill" = "xno" ; then
   enable_fill="0"
 else
@@ -727,6 +728,38 @@ if test "x$enable_utrace" = "x1" ; then
 fi
 AC_SUBST([enable_utrace])
 
+dnl Support Valgrind by default.
+AC_ARG_ENABLE([valgrind],
+  [AS_HELP_STRING([--disable-valgrind], [Disable support for Valgrind])],
+[if test "x$enable_valgrind" = "xno" ; then
+  enable_valgrind="0"
+else
+  enable_valgrind="1"
+fi
+],
+[enable_valgrind="1"]
+)
+if test "x$enable_valgrind" = "x1" ; then
+  JE_COMPILABLE([valgrind], [
+#include <valgrind/valgrind.h>
+#include <valgrind/memcheck.h>
+
+#if defined(__VALGRIND_MAJOR__) && defined(__VALGRIND_MINOR__)		\
+    && (__VALGRIND_MAJOR__ > 3 || (__VALGRIND_MAJOR__ == 3 &&		\
+    __VALGRIND_MINOR__ >= 6))
+#else
+#  error "Incompatible Valgrind version"
+#endif
+], [], [je_cv_valgrind])
+  if test "x${je_cv_valgrind}" = "xno" ; then
+    enable_valgrind="0"
+  fi
+  if test "x$enable_valgrind" = "x1" ; then
+    AC_DEFINE([JEMALLOC_VALGRIND], [ ])
+  fi
+fi
+AC_SUBST([enable_valgrind])
+
 dnl Do not support the xmalloc option by default.
 AC_ARG_ENABLE([xmalloc],
   [AS_HELP_STRING([--enable-xmalloc], [Support xmalloc option])],
@@ -1088,8 +1121,9 @@ AC_MSG_RESULT([prof-libgcc        : ${enable_prof_libgcc}])
 AC_MSG_RESULT([prof-gcc           : ${enable_prof_gcc}])
 AC_MSG_RESULT([tcache             : ${enable_tcache}])
 AC_MSG_RESULT([fill               : ${enable_fill}])
-AC_MSG_RESULT([xmalloc            : ${enable_xmalloc}])
 AC_MSG_RESULT([utrace             : ${enable_utrace}])
+AC_MSG_RESULT([valgrind           : ${enable_valgrind}])
+AC_MSG_RESULT([xmalloc            : ${enable_xmalloc}])
 AC_MSG_RESULT([dss                : ${enable_dss}])
 AC_MSG_RESULT([lazy_lock          : ${enable_lazy_lock}])
 AC_MSG_RESULT([tls                : ${enable_tls}])