Per the notes in bug #17168, updates which only affect sticky tags but which do not change file contents should not output a `U' status.

To demonstrate, `cvs up -rbranch && cvs up -A', with a branch that mirrors the content of the trunk.

This should be possible simple to do in update_fileproc.  Have patch_file set docheckout to -1 when there are no differences between the workfile and the new version.  Then, in update_fileproc, when docheckout == -1, skip calling server_updated and just abuse Checked-in response (perhaps via server_checked_in()) to send the entry to the client, as is already done in several other locations.

Unfortunately, this would really be an abstraction violation.  Classify_File should return T_ENTRY or the like if only the entry should be updated, but to do this would require some test checkouts, and to do that efficiently would require caching the checkouts for later use by patch_file or whatever.  All this would be a lot of work to get right.