Return PAM errors from mod_intercept_form_submit

Return PAM errors from mod_intercept_form_submit

This fixes several problems:

1. The PAM error was being retrieved from the wrong location
2. The error was not always logged properly
3. The error was not propogated up
4. Even if the error had been propgated up the auth_failed
   routine failed to pass it to the error page template.

A dictionary is used to translate the PAM errors into something
more consulable. This can be used eventually to translate
into other languages.

https://fedorahosted.org/ipsilon/ticket/69

Signed-off-by: Rob Crittenden <rcritten@redhat.com>
Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>