procedure
  For some functions returning strings (like "replace" and "ifnull" - where
  val_str() is returning a pointer into one of the parameters) - we ended
  up with a dangling pointer after the new operator destroyed the reuse item
  in the eval function.
  A working, if not very elegant, solution is to simply copy the string in
  such cases.


mysql-test/r/sp.result:
  New test case for BUG#13941.
mysql-test/t/sp.test:
  New test case for BUG#13941.
sql/sp_head.cc:
  Copy the string when evaluating some string functions (e.g. "replace" and "ifnull")
  to avoid using a dangling pointer.