LIKE expressions for sqlbuilder

* LIKE expressions in sqlbuilder
* A way to escape '%' and '_' for building LIKE right-hand-sides
* A modification to the standard string-escaping code so it doesn't escape a backslash before those same LIKE-special characters (backslashes are allowed to be literal there)
is this rule specific to only like pattern string (i.e., is it correct to not escape "\%" and "\_" in general)?