Ignore MALLOC_CONF in set{uid,gid,cap} binaries.

This eliminates the malloc tunables as tools for an attacker.

Closes #173

configure.ac

@@ -1108,6 +1108,24 @@ fi
 
 CPPFLAGS="$CPPFLAGS -D_REENTRANT"
 
+dnl Check if the GNU-specific secure_getenv function exists.
+AC_CHECK_FUNC([secure_getenv],
+              [have_secure_getenv="1"],
+              [have_secure_getenv="0"]
+             )
+if test "x$have_secure_getenv" = "x1" ; then
+  AC_DEFINE([JEMALLOC_HAVE_SECURE_GETENV], [ ])
+fi
+
+dnl Check if the Solaris/BSD issetugid function exists.
+AC_CHECK_FUNC([issetugid],
+              [have_issetugid="1"],
+              [have_issetugid="0"]
+             )
+if test "x$have_issetugid" = "x1" ; then
+  AC_DEFINE([JEMALLOC_HAVE_ISSETUGID], [ ])
+fi
+
 dnl Check whether the BSD-specific _malloc_thread_cleanup() exists.  If so, use
 dnl it rather than pthreads TSD cleanup functions to support cleanup during
 dnl thread exit, in order to avoid pthreads library recursion during