Fix XML encoding of 'identity display' in NOTIFY messages, continued.

When r378933 was merged into 1.8, it should have also escaped
remote_display, since it will have the same XML encoding problem when
the caller/callee roles are reversed.

(closes issue ABE-2902)
Reported by: Guenther Kelleter


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@379001 f38db490-d61c-443f-a65b-d21fe96a405b