Adding pidigits.py and parallelpi.py to examples.

Merging upstream.

Several small fixes during code review with Brian. - Delete stale ipcluster.py file. - Add default html target to docs makefile - Fix up a warning in api doc generation. - Fix bug with autocall (missing import) - Fix duplicate options in ipclusterapp.

Minor improvements to the parallel computing stuff. * Made various user messages better. * Added a longer (4s) paused before ipcluster exits.

Work on examples and fixed a super subtle bug in Component. * Recently, we stopped copying the config passed to a Component. This had a subtle side effect that mutable config attribute values were becoming class wide attributes. We are now doing a deep copy of all attributes as they are set on the Component instance.

Fixing how the working directory is handled in kernel. * Changed working_dir -> work_dir. * Now, ipcluster does not try to set the work dir for the controller and engine. To set it, just use the engine/controller config or pass the command line arg to the engine_args/controller_args attribute of a launcher.

Reworking how controller and engines startup in ipcluster. I have covered more edge cases robustly: * The engines will be shutdown if the controller dies. * If the cluster is shutdown, but the controller or engines are already dead, the exit is graceful. * The old .out and .err files created by the Windows HPC job scheduler are now removed before ipcluster starts.

Minor fixes to get Win HPC support working fully.

More work on the launchers and Win HPC support.

Doh. Fixed minor typo in last commit.