recent versions of msgpack break iohub keyboard.state

[isolver]

The demos/coder/iohub/keyboard.py demo does not receive keyboard events - appears to hang until demo timeout occurs. Initial debugging shows that the iohub keyboard.state property is failing on linux. This means demo's / experiments that use keyboard.getEvents() work, but any that use methods like keyboard.getPresses() currently fail on linux.

Env:

• Mint Linux 18
• anaconda python 3.6
• running latest psychopy master source

[isolver]

OK, looks like newer versions of msgpack do not support encoding / decoding integer dict keys (see msgpack/msgpack-python#410), which is what is used by the iohub keyboard.state dict. Need to convert int's to str keys for server response.

[isolver]

Can reproduce on win10 as well when using more recent version of msgpack.