Fix fork-related bugs.

Acquire/release arena bin locks as part of the prefork/postfork.  This
bug made deadlock in the child between fork and exec a possibility.

Split jemalloc_postfork() into jemalloc_postfork_{parent,child}() so
that the child can reinitialize mutexes rather than unlocking them.  In
practice, this bug tended not to cause problems.

src/base.c

@@ -4,7 +4,7 @@
 /******************************************************************************/
 /* Data. */
 
-malloc_mutex_t	base_mtx;
+static malloc_mutex_t	base_mtx;
 
 /*
  * Current pages that are being used for internal memory allocations.  These
@@ -104,3 +104,24 @@ base_boot(void)
 
 	return (false);
 }
+
+void
+base_prefork(void)
+{
+
+	malloc_mutex_prefork(&base_mtx);
+}
+
+void
+base_postfork_parent(void)
+{
+
+	malloc_mutex_postfork_parent(&base_mtx);
+}
+
+void
+base_postfork_child(void)
+{
+
+	malloc_mutex_postfork_child(&base_mtx);
+}