Rewrite instructions for building the uClibc toolchain, and
change install location of source tarballs.

Finally committed all of my Linux MFS stuff.  It's not done yet, but enough is there that I need to get it into version control before I lose it.

This includes:
- Build tree for a Linux frisbee MFS (the source tarballs are in ops:/share/linux/mfs/source)
- Patch for pxelinux to add bootinfo support
- Patch for grub to support our magic config sector