[merge tracking] Merge test #12: No-op merging of the svn:mergeinfo property

Merge test #12 was marked as XFAIL in r22119. I'd like some feedback
on what y'all think the expected behavior should be. Stripping out
the irrelevant stuff, here's the situation:

$ svn cp TRUNK_URL BRANCH_URL # create r2
$ # Do some other unrelated stuff to create r3
$ svn pg svn:mergeinfo BRANCH_URL@2
/A:1
$ svn pg svn:mergeinfo TRUNK_URL@3
$ svn di BRANCH_URL@2 TRUNK_URL@3

Property changes on: .
___________________________________________________________________
Name: svn:mergeinfo
   - /A:1

So, BRANCH_URL has some merge info, and trunk doesn't.

$ svn merge BRANCH_URL@2 TRUNK_URL@3 WC_PATH
 G svn-test-work/working_copies/merge_tests-12/A

A merge of the difference between these two URLs produces a delta,
which is a revert of some merge info which doesn't exist on TRUNK_URL,
nor happens to exist in WC_PATH (which happens to correspond to
TRUNK_URL). So, even though we have a delta, application of the delta
is a no-op.

Should we still send a mer' G'ed notification?