This patch reverts a change introduced by Bug 6951, which incorrectly
set thd->abort_on_warning for stored procedures.

As per internal discussions about the SQL_MODE=TRADITIONAL,
the correct behavior is to *not* abort on warnings even inside an INSERT/UPDATE
trigger.

Tests for Stored Procedures, Stored Functions, Triggers involving SQL_MODE
have been included or revised, to reflect the intended behavior.

(reposting approved patch, to work around source control issues, no review needed)