Support HTTP digest authentication for the http manager interface.

(closes issue #10961)
 Reported by: ys
 Patches: 
       digest_auth_r148468_v5.diff uploaded by ys (license 281)
       SVN branch http://svn.digium.com/svn/asterisk/team/group/manager_http_auth
 Tested by: ys, twilson, tilghman
 Review: http://reviewboard.digium.com/r/223/
 Reviewed by: tilghman,russellb,mmichelson


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@190349 65c4cc65-6c06-0410-ace0-fbb531ad65f3