hgit -> hgk.py

[Matt Mackall]

I've committed the following to tip:

Move hgit to hgk.py
- importing hgit as an extension created compiled hgitc, which was
confusing
- hgit existed to support hgk so it was slightly misnamed
- removed executable bit as we no longer run it directly
- add 'view' command so we can run hg view
- change git-* commands to debug-* so hg help won't show them
- chdir to repository root on view so hgk doesn't choke in subdirs


-- 
Mathematics is the supreme nostalgia of our time.