Fix the blame -g implemenation to no longer depend on false positives
in the file contents change detection.

* subversion/libsvn_client/blame.c
  (update_blame): Factored out from ...
  (window_handler): ... this.  Only do the diff application directly here. 
  (file_rev_handler): For potential merges, trigger the blame processing
                      even if there has been no change since the last rev
                      which might have been on a different branch.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1570936 13f79535-47bb-0310-9956-ffa450edef68