make S_OR and S_COR safe to use even if the parameters are function calls or have side effects. it still bothers me that these are called S_OR and not something like ast_string_or, but that's water over the bridge



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@155079 65c4cc65-6c06-0410-ace0-fbb531ad65f3