I was generating the POT file from the generated yelp.xml instead
of from the source yelp.xml.in. Since the generated file doesn't
have the ITS rules, <string/> was not withinText, so itstool used
a placeholder, so no translations actually matched.

I fixed the Makefile and all of the translations.

Also, I was using ALL_LINGUAS to create the POT file, just like
yelp-xsl does. But I wasn't setting ALL_LINGUAS in configure.ac.
Fixed.