Add functions to map syslog facilities and priorities constants to strings.

Also change the default casing of the string contants to lowercase.  This really
just saves us from have to lowercase them later when displaying them.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@203605 65c4cc65-6c06-0410-ace0-fbb531ad65f3