Make extension match characters case-insensitive.

(closes issue #12777)
 Reported by: jsmith
 Patches: 
       lower_case_patterns-trunk-v1.patch uploaded by jsmith (license 15)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@121010 65c4cc65-6c06-0410-ace0-fbb531ad65f3