Upgrade MySQL-python to 1.2.5

I was getting a build error with 1.2.4.  See:
http://stackoverflow.com/a/22821615/106302
Fix get_account_by_guid function

I don't have a good way to test this on older versions of GnuCash, but
the previous code worked on 2.4.11 and did not work on 2.6.3.