Fix potential VM map fragmentation regression.

Revert 245ae6036c (Support --with-lg-page
values larger than actual page size.), because it could cause VM map
fragmentation if the kernel grows mmap()ed memory downward.

This resolves #391.

include/jemalloc/internal/jemalloc_internal.h.in

@@ -754,7 +754,7 @@ sa2u(size_t size, size_t alignment)
 		 * Calculate the size of the over-size run that arena_palloc()
 		 * would need to allocate in order to guarantee the alignment.
 		 */
-		if (usize + large_pad + alignment <= arena_maxrun)
+		if (usize + large_pad + alignment - PAGE <= arena_maxrun)
 			return (usize);
 	}
 
@@ -784,7 +784,7 @@ sa2u(size_t size, size_t alignment)
 	 * Calculate the multi-chunk mapping that huge_palloc() would need in
 	 * order to guarantee the alignment.
 	 */
-	if (usize + alignment < usize) {
+	if (usize + alignment - PAGE < usize) {
 		/* size_t overflow. */
 		return (0);
 	}