Issue547: fixes pysh profile and creates pysh extension

This is my proposed fix for a very old issue: https://github.com/ipython/ipython/issues/547


> there's an open bug / broken code in master, at minimum the bug and related issues should be wont-fix not wish-list

Sorry about that - the bug was opened when it was removed, and we thought people would be keen to get this back. It's lingered without really getting any attention.

> if this extension doesnt belong in the main ipython distro.. well, does any extension? 

Quite possibly not - the point of extensions is that they don't have to be in master. Of the extensions in that folder, parallelmagic is just a deprecation warning; cythonmagic, rmagic and sympyprinting are being moved out to their separate projects; storemagic was an attempt of mine to use the extensions framework for greater modularity within IPython, and autoreload is probably there just for historical reasons.

I think it makes sense to have some amount of shell-like functionality within IPython, like `!foo` and aliases for things like `ls`. I suspect we could give up the `x = !ls` syntax without too many complaints - I've only seen it used as a party trick - but since it's already there and doesn't seem to interfere too much, why bother ripping it out?

I think it makes sense to maintain pysh as an external project - especially since I see you're already maintaining [smash](https://github.com/mattvonrocketstein/smash), which builds on top of pysh. But I'll give other developers a chance to chime in.