Improve BSD licensed text-processing tools

[Jesse Hagewood]

Some milestones made last week:

- Fixed textfile detection in diff3, using the same methods I used with
diff.
- Fixed several bugs I have found in diff3.
- Wrote a test script for diff3.

I've been looking at how to integrate the diff utilities more tightly by
studying grep, and while I'm not sure how to improve tighter integration
between diff/sdiff/diff3, I have an idea to integrate utilities for
different file formats such as zdiff into diff the same way that grep does
with the different grep utilities. I plan on implementing it this
afternoon.

Last week, I also began looking at diff3. The main issue here is the piping
to diff is unimplemented. I plan on doing this in a similar way that sdiff
has. Most functionality is there in diff3, except for a few missing
features. The majority of the week I will be focused  on this.

Sdiff is looking very good right now. I'll comb through the code to fix
compiler warnings and style issues, and run some benchmark tests. Also, in
all of sdiff's files, there is only a comment saying it is public domain.
Should the BSD license be added to the files?