po: reapply local e2fsprogs chages to po/Makefile.in.in

po: reapply local e2fsprogs chages to po/Makefile.in.in

These are the changes which are needed after running gettextize to
update to gettext 0.19.8 in the previous commit.

 * Add support for maintainer mode (which doesn't do as much given
     that gettext now has settings in Makevars which allows us to
     suppress automatic updates of the po and gmo files)
 * Add support to expand the '@' abbreviations in e2fsck/problem.c
     and give an explanation of how they work for translators
 * Add support for configure --enable-verbose-makecmds and default to
     "kernel-style" quieter make output --- this makes it easier
     to see warnings and errors by suppressing the distracting
     details.
 * Teach the makefile where to find the generated error table C files
     in the build directory.
 * Add make targets (e.g., all-static, fullcheck, coverage.txt) which
     are required by the top-level Makefile.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>