Composite table keys with non-existent XPATH target now Null

When specifying a composite table key it has been observed that some of the values of the key may not exist.  This is seen in chassis hardware.
In the event of an unfound XPATH the key value in the tuple is now None
Original behaviour was an uncaught exception.
Update device for ncclient 0.4.2 sshconfig support
Merge pull request #303 from shermdog/proxycommand

Update device for ncclient 0.4.2 sshconfig support
catch TimeoutExpiredError thrown by ncclient.
catch TimeoutExpiredError thrown by ncclient.
Added support for version_info into JSON and YAML
Fixed JSON support for RPC
version_info unit tests
unittest2 dev req
Merge pull request #298 from shermdog/table-missing-xpath

Composite table keys with non-existent XPATH target now Null
Added xml_rpc function to fetch XML RPC of a CLI command
Merge pull request #305 from shermdog/288

Fix for #288
Merge remote-tracking branch 'upstream/master' into cli-warning
Renamed to display_xml_rpc
Merge pull request #306 from shermdog/cli-warning

Added display_xml_rpc function to fetch XML RPC of a CLI command
added timeoutDecorator for execute (print still enabled)
Removed print debug from timeoutDecorator
Merge branch 'master' of https://github.com/tamihiro/py-junos-eznc into timeout_dec
Added timeout exception, tests
Merge pull request #307 from shermdog/timeout_dec

Added per-RPC timeout value and exception