[PATCH] test suite: Raise tree.SVNTreeUnequal exception

Hello,

There was a hack to define tree.SVNTreeUnequal exception handler from
svntest.main library. Please find attach a patch to fix this. With this
patch, we removed the definition in svntest.main library and use it
directly from svntest.tree library.

[[
Do not define SVNTreeUnequal exception handler in svntest.main library.
It can be used directly from svntest.tree library, where it is
originally defined.

* subversion/tests/cmdline/svntest/main.py
  Do not import "tree" library and do not define SVNTreeUnequal
  exception handler here.
* subversion/tests/cmdline/merge_tests.py
  (merge_singleton_handler): Raise tree.SVNTreeUnequal() exception.
* subversion/tests/cmdline/update_tests.py
  (detect_extra_files): raise tree.SVNTreeUnequal() exception.
]]

-- 
Regards,
Bhuvaneswaran