Add trace flag for configuring long stack traces

[dougwilson]

This adds a new connection option trace to control if long stack traces are generated. The default if not specified is to generate them, which keeps the default behavior the same.

This also makes a minor tweak on how the initial stack is generated. Before it was generated in the Sequence constructor, so it captured the stack at the time the protocol sequence was generated. The stack is now captured in Protocol.prototype._enqueue. In all cases within the public API this captures the same stack, except there will be the extra call to _enqueue at the top of the stack. The following case, though, will be positively altered:

var mysql = require('mysql');
var connection = mysql.createConnection(...);

connection.connect();

connection.query('FAIL', function (err) { // 1
  if (err) throw err;
  // Stack trace will include the line marked 1, as expected
});

var query = connection.createQuery('FAIL'); // 2

connection.query(query, function (err) { // 3
  if (err) throw err;
  // Stack trace will include the line marked 3
  // Prior to this it would include the line marked 2
});

The change of the call site capture essentially moves the stack when using require('mysql').createQuery from the call to createQuery to the actual location where the query was handed over to the connection.

closes #710

[sidorares]

👍

[felixge]

💖 👍

[sidorares]

published as v2.0.1 (could be 2.1 as it's new api, but I think due to defaults it more like patch level bump)