shm_unlink(name) is the proper way to close a shared memory in linux.
Prior to this, xenia was creating and not cleaning up shared memory handle
which would accumulate in /dev/shm. shm_unlink is the proper way of doing
this.
Add filename to CloseFileMappingHandle signature.
Add simple test to open and close.
CreateFileMappingHandle now takes shared memory name without a prefix.
The doc of shm_open recommends not using slashes and prefixing with "/".
The prefixing has been moved to the os implementation layer.
Invocations of CreateFileMappingHandle were all using "Local\\" so these
prefixes were removed.
