Make git more usable

This series allows to install the essential functionnality of git while still consuming as less space as possible. Space-consuming binaries are split to separate ipk's.

The final patch activates installation of gitk - it is only partially working, but does not force build of anything that's not built in the default shr image, and can hopefully bring someone into looking at what seems to be an issue in tcl/tk packaging.

Any specific reason you want to use dotted notation for PRs? While it's legitimate, it maybe confusing with INC_PR or DISTRO_PR...

Denys