More i18n tools tweaks:
* Remove difflib's quick_ratio() call, from quick tests looks it is four times slower than ratio(), and yet it gives the same results...
* Moved code to find all po's in a dir into its own func (will be used by i18n addon tools too).

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56132 954f8c5b-7b00-dc11-b283-0030488c597c