[swig/ruby bindings] Remaining test failures (post branch merges)

Kou, there were some Ruby test failures introduced by the code from
the sparse-directories and merge-tracking merges. I've corrected all
the problems from the sparse-directories merge, but test_merge and
test_merge_peg are failing on trunk as a result of the merge of the
merge-tracking branch. I'm attaching a patch which fixes this problem
(which is caused merge info inherited from the root of the WC's trunk
directory avoiding a repeated merge), but was wondering if this your
desired approach, or whether an alternate approach would be more
appropriate.

- Dan