remove hardcoded CDR() support from pbx_builtin_setvar_helper in favor of...

remove hardcoded CDR() support from pbx_builtin_setvar_helper in favor of already-implemented CDR() function
make SetVar() options actually work as documented
remove SetVar() 'c' and 'r' options, since the CDR() function can provide this functionality
add 'r' option to CDR() function to control recursive retrieval/storage
(inspired by bug #4143, but without the SetVar syntax changes)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@5574 65c4cc65-6c06-0410-ace0-fbb531ad65f3