Check if AGGREGATE was given with a stored (non-UDF) function, and return
  error in that case.
  Also made udf_example/udf_test work again, by adding a missing *_init()
  function. (_init() functions required unless --allow_suspicious_udfs is
  given to the server, since March 2005 - it seems udf_example wasn't updated
  at the time.)


mysql-test/r/sp-error.result:
  Updated results for BUG#16896.
mysql-test/t/sp-error.test:
  Added test case for BUG#16896.
sql/share/errmsg.txt:
  New error message: ER_SP_NO_AGGREGATE
sql/sql_yacc.yy:
  Check if AGGREGATE was used when creating a stored function (i.e. not an UDF).
sql/udf_example.cc:
  Added myfunc_int_init() function to make it work when the server is running without
  --allow_suspicious_udfs.