add an automatically generated Asterisk log message if the allocation fails
for some reason.  Otherwise, they are functionally the same, with the
exception of ast_strdup and ast_strndup.  These functions have the added
ability to accept a NULL argument without error, which will just be ignored
without generating an error. The coding guidelines have also been updated to 
reflect all of this information.  (issue #4996)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@7952 65c4cc65-6c06-0410-ace0-fbb531ad65f3