po: Fix replacement of %m in sed programs

po: Fix replacement of %m in sed programs

When running make dist, I hit this error:

  rm -f en@arabic.gmo && /usr/bin/gmsgfmt -c --statistics --verbose -o en@arabic.gmo en@arabic.po
  en@arabic.po:5312: 'msgstr' is not a valid C format string, unlike 'msgid'.
  Reason: The character that terminates the directive number 3 is not a valid conversion specifier.
  /usr/bin/gmsgfmt: found 1 fatal error

This was caused by "%m" being replaced with foreign Unicode characters.
For example:

  msgid "cannot rename the file %s to %s: %m"
  msgstr "ﺹﺎﻨﻧﻮﺗ ﺮﻌﻧﺎﻤﻋ ﺖﻬﻋ ﻒִﻴﻠﻋ %s ﺕﻭ %s: %ﻡ"

Mimic the workaround used for "%s" by reversing the replacement of "%m" at
the end of the sed programs.

Signed-off-by: Mike Gilbert <floppym@gentoo.org>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>