s3-vfs: split @GMT token filter code into a common .c

[David Disseldorp]

Hi,

I've recently been working on a Snapper vfs module[1] to propagate FSRVP
snapshot create/delete requests to snapperd via D-Bus.

The module makes use of @GMT token filtering hooks currently provided by
vfs_shadow_copy2. Therefore, I'd like to split these hooks into a
common source for use by both modules, similar to the current
relationship between vfs_acl_tdb.c, vfs_acl_xattr.c and vfs_acl_common.c

Please see following patch. Feedback appreciated.

Cheers, David

1) vfs_snapper module code:
	http://git.samba.org/?p=ddiss/samba.git;a=blob;f=source3/modules/vfs_snapper.c;h=d45121b2de6f799af322071e931a2f6affc72bf0;hb=6a3d29812485f1dfb511ff548d5c81f2406e4eb8
   Demonstration / shameless self promotion:
	http://bambuser.com/v/3081954#t=9331s