Modify pages_map() to support mapping uncommitted virtual memory.

If the OS overcommits:
- Commit all mappings in pages_map() regardless of whether the caller
  requested committed memory.
- Linux-specific: Specify MAP_NORESERVE to avoid
  unfortunate interactions with heuristic overcommit mode during
  fork(2).

This resolves #193.

include/jemalloc/internal/pages.h

@@ -9,13 +9,14 @@
 /******************************************************************************/
 #ifdef JEMALLOC_H_EXTERNS
 
-void	*pages_map(void *addr, size_t size);
+void	*pages_map(void *addr, size_t size, bool *commit);
 void	pages_unmap(void *addr, size_t size);
 void	*pages_trim(void *addr, size_t alloc_size, size_t leadsize,
-    size_t size);
+    size_t size, bool *commit);
 bool	pages_commit(void *addr, size_t size);
 bool	pages_decommit(void *addr, size_t size);
 bool	pages_purge(void *addr, size_t size);
+void	pages_boot(void);
 
 #endif /* JEMALLOC_H_EXTERNS */
 /******************************************************************************/