extend ramfs so it can take an initial cpio (via cpio) and an existing root directory
extend ramfs so it can take an initial cpio (via cpio) and an existing root directory

Try it:
go run ramfs.go -d -removedir=false -cpio ../tinycorebase/corepure64.cpio -test

This will remove all files in /bin that are u-root commands.
The /init from the initramfs will be moved to /init.orig

TODO: test to see if an existing init is there, since there may not be one.
TOOD: modify our init to test for init.orig and run it if it is there.

This allows us to build on a tinycore or other initramfs.

There are a few sanity checks but more are needed.

I've tested it and it works just as Alex wants (I hope).

Note: it's still a little rough. It needs a few tweaks to make it easy to run.
It's picky about the setting of GOROOT and GOPATH. Also, it should run
GOROOT/bin/go, not just go, since you may have the wrong Go in your PATH.

Change-Id: I569157cfd6288f53ce6cabcfb9f81bbf64b60613
Signed-off-by: Ronald G. Minnich <f569d0af9a3481c4007b95c7180d6c41009f2513@gmail.com>

hugelgupf/u-root,u-root/u-root,rminnich/u-root,GanShun/u-root,GanShun/u-root,hugelgupf/u-root,hugelgupf/u-root,GanShun/u-root,u-root/u-root,rminnich/u-root,rminnich/u-root,rminnich/u-root,u-root/u-root,hugelgupf/u-root