The auto-inc unsafe warning makes sense even though it's just
one auto-inc table could be involved via a trigger or a stored
function.
However its content was not updated by bug@45677 fixes continuing to mention
two tables whereas the fixes refined semantics of replication of auto_increment 
in stored routine.

Fixed with updating the error message, renaming the error and an internal unsafe-condition 
constants.

A documentation notice
======================

      Inserting into an autoincrement column in a stored function or a trigger
      is unsafe for replication.
      Even with just one autoincrement column, if the routine is invoked more than 
      once slave is not guaranteed to execute the statement graph same way as 
      the master.
      And since it's impossible to estimate how many times a routine can be invoked at 
      the query pre-execution phase (see lock_tables), the statement is marked
      pessimistically unsafe. 



mysql-test/suite/binlog/r/binlog_stm_unsafe_warning.result:
  results updated to include the expected unsafe warning.
mysql-test/suite/binlog/t/binlog_stm_unsafe_warning.test:
  regression test for bug#50192 to diplaying the unsafe warning comes out to the user warning stack.
sql/share/errmsg-utf8.txt:
  Updating the auto-inc unsafe message to correspond to bug@45677 fixes' new sematics.
sql/share/errmsg.txt:
  Updating the auto-inc unsafe message to correspond to bug@45677 fixes' new sematics.
sql/sql_base.cc:
  changing a symbolic name to correspond to updated by bug@45677 fixes new sematics.
sql/sql_lex.cc:
  changing a symbolic name to correspond to updated by bug@45677 fixes new sematics.
sql/sql_lex.h:
  changing a symbolic name to correspond to updated by bug@45677 fixes new sematics
  and description comments.