We started using "%" PRItime, imitating "%" PRIuMAX and friends, as
a way to format the internal timestamp value, but this does not
play well with gettext(1) i18n framework, and causes "make pot"
that is run by the l10n coordinator to create a broken po/git.pot
file.  This is a possible workaround for that problem.

* jc/po-pritime-fix:
  Makefile: help gettext tools to cope with our custom PRItime format