Allow database password to be NULL and several other cleanups.

(closes issue #12048)
 Reported by: bukaj
 Patches: 
       20080222__bug12048.diff.txt uploaded by Corydon76 (license 14)
 Tested by: bukaj


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@104036 65c4cc65-6c06-0410-ace0-fbb531ad65f3