[Toybox] Implemented split, pondering a release.

[Rob Landley]

I actually got some time to myself this weekend (visited my sister  
while the kids were at their father's and she was at work for part of  
it), so I banged out one of the remaining low-hanging-fruit commands  
that aboriginal linux (actually linux from scratch) needs to build:  
split. Got it finished, tested, and checked in, and added tests for it  
to the test suite.

Starting to think about a release. I've got to do an aboriginal linux  
release for the 3.10 kernel in a couple weeks, and I generally flush  
pending toybox stuff into a release so that can use it. (Three fewer  
busybox commands, 42 left several of which are duplicates like "[ [[  
test" and "ash sh", and of course the toybox multiplexer.)

I'd like to finish the ifconfig cleanup, and documenting all that.  
Beyond that nothing's really a release blocker, but I'm open to  
suggestions.

(I feel hugely guilty about not getting mount.c looked at. That's  
probably the first thing up for next release. Well, I have a  
half-finished umount.c that I might do first because it's smaller and  
the three mount/umount/losetup are sort of a group. To do mount I need  
to set up test environments for nfs and samba, and finally get the root  
support in scripts/test so I can do a mount.test...)

Rob