Request for review(XXS): 6838842 NUMA allocator: Segfault during startup on Linux

[Igor Veresov]

The semantics of os::free_memory() has changed with the fix for 6541756 
(Reduce executable C-heap). This function is used in the NUMA-aware 
allocator to free pages. Instead, now it does an mmap(PROT_NONE), which 
causes the VM to trap on the next access. The fix is to change this 
function to have its original semantics.

Webrev: http://cr.openjdk.java.net/~iveresov/6838842/webrev.00