Now, typing "make zip-file" will create a standard zip-file for each
extension, with everything necessary, including translations and GSettings schemas.
These files can then be installed with the tweak-tool or uploaded
at extensions.gnome.org
Based on an earlier patch by Jasper St. Pierre.
Cherry-picked from master. The zip file contains everything that is
needed for extensions, but schemas and translations are not loaded
from there, as convenience.js cannot be supported in 3.2
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