Escape backslashes in like arguments

Like conditions with backslashes in them do not currently work. In like arguments, literal % and _ are escaped, but the escape character (\) should also be escaped (doubled).

> To match a literal underscore or percent sign without matching other characters, the respective character in pattern must be preceded by the escape character. The default escape character is the backslash but a different one can be selected by using the ESCAPE clause. To match the escape character itself, write two escape characters.
http://www.postgresql.org/docs/9.3/static/functions-matching.html