[merge]problems with committing merges in a dirstate tree with a symlink

[Martin Pool]

Martin Pool has voted +1 (conditional).
Status is now: Conditionally approved
Comment:
-                else:
-                    assert 'unknown kind'
+                elif kind != 'symlink':
+                    assert False, 'unknown kind'

While this fix is correct I'd like in general to make assertion messages 
have a bit more information.  Users do hit them and report bugs from 
time to time.  If you included the actual kind, then the error report 
will be a bit more useful and we will avoid one roundtrip to the user.

Also you might as well just raise AssertionError if it's done 
unconditionally.

I like the tearDown tests.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20070312210354.GA3819%40cyclops.localdomain%3E