if the function, invoked in a non-binlogged caller (e.g. SELECT, DO), failed half-way on the master,
slave would stop and complain that error code between him and master mismatch. 
To solve this, when a stored function is invoked in a non-binlogged caller (e.g. SELECT, DO), we binlog the function
call as SELECT instead of as DO (see revision comment of sp_head.cc for more).
And: minor wording change in the help text.
This cset will cause conflicts in 5.1, I'll merge.