If libmthread runs into a memory allocation failure while attempting
to enlarge its thread pool, it does not free up any preliminary
allocations made so far.
Reported by dcb314.
This closes#152.
Change-Id: Ib882a4544e4802a0eb0a53446b43997876cde633
Edited by David van Moolenbroek to deallocate the guard page as well.
Note that while the new approach is better in theory (previously, the
hole could end up being filled by another allocated page), guard page
protection is now broken in practice, because VM does not support
setting specific page permissions (in this case, PROT_NONE).
Change-Id: I882624f5d152d3ebe82fca649cbad85aa4931780