- The argument to "ESCAPE" of a LIKE operator or similar

- The argument to "ESCAPE" of a LIKE operator or similar
is passed through render_literal_value(), which may
implement escaping of backslashes.  [ticket:1400]
- Postgresql render_literal_value() is overridden which escapes
backslashes, currently applies to the ESCAPE clause
of LIKE and similar expressions.
Ultimately this will have to detect the value of
"standard_conforming_strings" for full behavior.
[ticket:1400]
- MySQL render_literal_value() is overridden which escapes
backslashes, currently applies to the ESCAPE clause
of LIKE and similar expressions.   This behavior
is derived from detecting the value of
NO_BACKSLASH_ESCAPES.  [ticket:1400]