`queue: false` checkout can incorrectly error in poolboy pool

[fishcakez]

During client check in:

• Old client sends check in to poolboy
• Poolboy receives check in and assign new client
• New client sends queue: false check out request to Connection
• Connection receives check out but it think old client still holds socket so replies with error
• Old client sends check in to Connection
• Connection receives check in

Similar can happen on disconnect check in with queue: false but that is likely desired as connection not immediately available. However if queue: true:

• Old client sends check in to poolboy
• Poolboy receives check in and assign new client
• New client sends queue check out request to Connection
• Connection receives check out and queues request
• Old client sends disconnect to Connection
• Connection sends error to queue and disconnects/connects

However if we the old client sends disconnect to Connection before checking in to poolboy (not current behaviour) the disconnect/connect would always arrive before the new client checkout. This means the new client would always be blocked waiting for the connection, which may or may not succeed.

[fishcakez]

Fixed in efe1f8a6e2ccc7d59a1ad0d986c0261fa6f18c0e