Merge PR
#847 (connection files)
* JSON connection files are now used to connect files
* HMAC message signing is now on by default in all IPython apps
* Adds IPython.lib.kernel, which contains utility functions for connecting
clients. These were mostly copied out of qtconsoleapp in order to be
more general.
* Adds %connection_info and %qtconsole magics to zmqshell
closes gh-688
closes gh-806
closes gh-691