Update bash to patch release 20

I just felt like updating bash. Not because some heavy security bugs have been found ;)

As already stated in the [info mail](http://comments.gmane.org/gmane.comp.version-control.msysgit/20944) on the msysgit mailing list, I've included, against our rules, some binary files to compile bash.
But as msysgit is basically EOL, I hope this is okay.

Once this is merged I'll cherry-pick 895e4dd to msysgit/master on my own. Okay?