Update Pool.js to allow calling Pool.prototype.query with no callback

[wizardfrag]

Add a check in Pool.prototype.query to see if the callback is a function, to allow calling it with no callback specified (i.e. for UPDATE/INSERT type queries)

[felixge]

Wouldn't it be simpler to do: cb = cb || function() {} on top of the function?

[dougwilson]

Or at the very least cb && cb(null) type construct, as the typeof may mask mistakes like accidentally passing a string in the callback argument.

[tolgaek]

Yeah I think that's more of a standard that I see more and it can be used with the return statement that he has in his patch return cb && cb();

[tellnes]

Do we really want to silently swallow any errors in this case?

[dresende]

That's up to the user.