vmem: add the malloc_rwlock_t type
vmem: change type of pool->arenas_lock to malloc_rwlock_t
vmem: fix race condition in je_mallocx()

Ref: pmem/issues#15
common: fix make test in src/Makefile
util: remove invalid pool file of util_pool_create()

If someone tries to create a pool of size greater than the maximum
available space, posix_fallocate() fails but it leaves an invalid
file which should be removed.
Merge pull request #78 from ldorau/common-fix-make-test-in-src-Makefile

common: fix make test in src/Makefile
Merge pull request #79 from ldorau/vmem-fix-sporadic-segfault-in-MALLOCX_ARENA-ut

vmem: fix sporadic segfault in MALLOCX_ARENA unit test
vmem-fix-stats-with-custom-funcs

Fix to not create pool 0 for vmem_stats()
when custom functions were provided.
Merge pull request #80 from ldorau/util-remove-invalid-pool-file-of-util_pool_create

util: remove invalid pool file of util_pool_create()
Merge pull request #82 from spawlows/vmem-fix-stats-with-custom-funcs

vmem-fix-stats-with-custom-funcs