feature request: expose message validation in libgettextpo

[James Henstridge]

The libgettextpo library provides a po_message_check_format() function
for performing format string checking on a po_message_t.  However this
is not the only message validity check that the gettext tools perform.

The msgfmt program performs some other checks, such as consistent use of
newlines at the beginning and end of strings.

A po_message_validate() function that performed all these checks would
be useful to programs that use libgettextpo to generate or edit PO
files.  As it is now, such applications either need to reimplement the
checks or omit them and risk producing broken PO files (and
reimplementing the checks is not ideal -- if gettext gets new checks,
the application needs to be updated too).

James.