Option -m NAME is interpreted as directory name if we can statfs() it
and its on hugetlbfs.  Else it's interpreted as POSIX shared memory
object name.  This is nuts.

Always interpret -m as directory.  Create new -M for POSIX shared
memory.  Last of -m or -M wins.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <1458066895-20632-4-git-send-email-armbru@redhat.com>
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>