CBD-979: Revert file_name_utils to C

There seems to be a bug in the mingw compiler causing the build
to fail on windows.

Change-Id: I9e34a34d4e698c8c333ceee1681915f5062fd259
Reviewed-on: http://review.couchbase.org/29380
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>