bug: if .connect() called more than once, incorrect callbacks are used

[fedor]

@ceejbot,

if FiveBeansClient.prototype.connect() called more than once, a callback for an old socket command may exist in self.handlers even after a new socket is created. In this case, the first command with the new socket will stuck, because its callback will not be called (a callback for the old socket will be called instead).

Suggested fix: #132.

[japod]

@ceejbot although this bug could be easily worked around in user code, since there is a PR ready, could you please consider merging it? The bug is quite annoying as the client generates misleading errors after just re-connecting.