Log Message:
Update to 0.27.0

Lots of bug-fixes and changes. Eg.:
* fixed 'svn merge':
     . (r6447,#1402) -r FOO:PREV works correctly
     . (r6452,#1379) no longer prints confusing no-op lines
     . (r6500/6503,#1399) warn user when a tree-delta chunk can't be applied
* cvs2svn.py:  lots of bugfixing related to branch/tag support
* fixed 'svn diff' and 'svn merge':
     . (r6604, #1311) diff URL URL on files now works
     . (r6668, #1142) diff comparing wc to repos branch
     . (r6687, #1297) diff/merge interaction in file adds
     . (r6703, #1319) merge problem with adding subtrees
     . (#6607) new default ancestry-following behavior for diff, merge

(Have a look at CHANGES for a complete list.)

OK'ed by epg@