function compareMessagesByLocation(a, b) {
	return a.line - b.line || a.column - b.column;
}
Compares items in a messages array by line and column.
@param {Message} a The first message.
@param {Message} b The second message.
@returns {number} -1 if a comes before b, 1 if a comes after b, 0 if equal.
@private