Extend issue #3067 test to cover the following case.
Extend issue #3067 test to cover the following case.

'When subtree with differing mergeinfo has been deleted at revision2(in case
of forward merge of revision1:revision2), system should somehow identify
the correct line of history' or atleast should be smart enough to 
understand the situation.

* subversion/tests/cmdline/merge_tests.py
  (dont_merge_revs_into_subtree_that_predate_it): Extend the test as 
   explained above.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion