files missing from po/POTFILES.in

[Sven Joachim <svenjoac@gmx.de>]

While working on the German dpkg translation, I noticed that there are
at least two files with translatable strings that are not listed in
po/POTFILES.in, namely lib/subproc.c and src/pkg-show.c.  As a
consequence, strings in these files are marked as obsolete in po/*.po
and are not translated in program output.

It seems this is a mistake that happened while moving functions around,
since both files are new in dpkg 1.15.0.  Someone™ should add them to
po/POTFILES.in.

Regards,
        Sven