Fix make distcheck errors using intltool

Dan Nicholsonrequested to merge
dbn/intltool:clean-cache-lock into debian/latest

When intltool-merge is used with the patch from #950444, it will leave behind a lock file. This is not cleaned up by the supplied Makefile.in.in stub and causes make distcheck to fail in projects using intltool.

Closes: #991623

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