R1:ff2b58dab746

Fix MySQL column escaping

Summary:
MySQL doesn't treat `\` as escaping character in ##``##.
This isn't probably SQL injection hole because I've found no calls of this method with user input.
But better safe than sorry.

See also [[http://dev.mysql.com/doc/refman/5.1/en/server-sql-mode.html#sqlmode_no_backslash_escapes | NO_BACKSLASH_ESCAPES]].

Test Plan:
lang=sql
SELECT `a\`b`; -- Throws: Syntax error near '`'.
-- Should throw: Unknown column 'a`b'.

Reviewers: epriestley

Reviewed By: epriestley…