vmem: add vmem_malloc_usable_size() to API
Merge pull request #70 from spawlows/vmem-add-malloc-usable-size

vmem: add vmem_malloc_usable_size() to API
vmem: fix freeing memory by iqalloct()

In case of huge pages iqalloct() calls huge_dalloc() for the pool #0
(src/jemalloc/include/jemalloc/internal/jemalloc_internal.h.in:834),
but huge_dalloc() should be called with the pool 'arena->pool'
as an argument in functions huge_ralloc(), arena_ralloc()
and iralloct_realign().

Add two functions: pool_iqalloct() and pool_idalloct() in order
to be able to pass a 'pool' argument from pool_iqalloct()
to huge_dalloc().

Ref: pmem/issues#8
Merge pull request #72 from ldorau/vmem-fix-freeing-memory-by-iqalloct

vmem: fix freeing memory by iqalloct()