r13714: Set MOUNT_CIFS_VENDOR_SUFFIX if _SAMBA_BUILD_ is set to

r13714: Set MOUNT_CIFS_VENDOR_SUFFIX if _SAMBA_BUILD_ is set to
"-"SAMBA_VERSION_OFFICIAL_STRING"-"SAMBA_VERSION_VENDOR_SUFFIX if
SAMBA_VERSION_VENDOR_SUFFIX is set or "-"SAMBA_VERSION_OFFICIAL_STRING
only if MOUNT_CIFS_VENDOR_SUFFIX is undefined.

This results in: mount.cifs -V
mount.cifs version: 1.10-3.1.2pre1-SVN-build-13706-foovendor
or
mount.cifs version: 1.10-3.1.2pre1-SVN-build-13706

Steve: If this is to long or you do not like it, we might add something
lile -VV to report the added part.
(This used to be commit 3c277c7a3cce14f185db7fede7c0c4ab77769670)