Fix for make unportability
88dad06b47eb80f699211c9b0b7a1c6d9016ad19 contains a make $(shell)
construct that apparently confuses older GNU make versions (possibly
because of the # inside the shell command?). This construct, which
would allow # comments inside LINGUAS files, was adapted from gettext
recommendations, but we don't actually need that functionality, so
sidestep this whole issue by just using plain "cat".
In passing, make this code work with vpath.