Fix the last commit.
gettextize: Use autoconf trace to detect auxdir and m4dir
autopoint: extract macro directories from configure.ac
po-mode: make (po-check-file-header) optional (bug #30835)

po-mode would always overwrite the PO Header Entry when editing *.po
files. This isn't always desired behavior as noted in bug #30835 so
it's now customizable.

It can be customized through the po-auto-update-file-header variable,
which can be t, nil or 'ask. It's t by default to preserve the old
default behavior.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
po-mode: Properly highlight C format strings with parameter positions
Update copyright year.
Update copyright year.
Fix msgctxt Glade2 support.
Augment testing for Glade2 UI files.
Support for GtkBuilder UI files.

Fix Savannah bugs #29216, #29900 and #34506.
Tests for GtkBuilder UI files.
Document GtkBuilder UI files support.
Update to upstream 0.18.2.1.