Remove gourmet/importers/mealmaster_importer.py from po/POTFILES.in.
Avoid a KeyError when pressing Enter on an empty search entry.
Simplify a conditional expression.
Remove obsolete file gourmet/PngImagePluginUpToDate.py.
Remove obsolete comment.
Backup when upgrading the DB to v0.16.
Move *.gourmet-plugin files to plugins/, install to share/gourmet/plugins.

This is required for python-distutils-extra to be able
to translate and install *.gourmet-plugin files properly.