Branch filter wildcards

This should address Issue 1285
https://github.com/gitextensions/gitextensions/issues/1285

Added support for shell glob wildcards via the log command's --branches=<pattern> option.
http://git-scm.com/docs/git-log (see --branches)

Works well. The only downside, and this is git behavior, is that if the pattern specified doesn't match anything, you get a single line result for the current branch, which can be a bit visually confusing. Still the functionality is worth that minor caveat. 

- Greg