Commit Finished -> Merge button enhancements

[Josh Kelley]

The Merge button that was added to the Commit Finished dialog (
https://code.google.com/p/tortoisesvn/issues/detail?id=232) is a great
idea, but compared to manually merging, it has a couple of disadvantages.

First (and minor), manually merging creates a complete entry under "Recent
messages" that consists of "Merged revision(s) ... from ...:" and the log
message of the merged revision. The Merge button creates an entry
consisting only of "Merged revision(s) ... from ...:", so I have to go
under "Recent messages" twice to get a complete commit message.

Second (and major), the Merge button doesn't update mergeinfo on the
top-level directory, so if I later look at the log, the revision doesn't
show up as already merged. (It looks like there are a couple of comments
at https://code.google.com/p/tortoisesvn/issues/detail?id=232 that also
describe this issue.)