Add localization support to com_err

Add localization support to com_err

* Add compile_et arguments --textdomain and --localedir.
* Store text domain and localedir at the end of error tables.
* error_message() calls dgettext if the table has a text domain.
* add_error_table() calls bindtextdomain if the table has a localedir.
* Define N_() as no-op in generated source and mark up error messages.
* When using system compile_et, test for --textdomain support.
* Use --textdomain option when available.
* Run xgettext over generated sources in compile_et rule.
* Translate com_err results in krb5int_get_error() if com_err won't.

ticket: 6918

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@24960 dc483132-0cff-0310-8789-dd5450dbe970