Improve BSD licensed text-processing tools

[Jesse Hagewood]

This week, I have implemented the following:

- While testing sdiff, I noticed that it would not accept binary files. GNU
sdiff will output the difference of binary files the same way as diff, with
a message simply saying the files differ. I implemented this in a similar
way to diff and diff3, and also have a function where it will execute a
diff process with only the input files if there is a binary file.

- Fixed all warnings generated when building sdiff.

- I've nearly completed zdiff integration in diff, however, I'm getting
weird compiler errors with undefined references to functions in zlib.h,
even though it is included. I'll try to resolve these errors this
afternoon. Also, I still need to change the Makefile to build both a "diff"
and a "zdiff" binary. This feature is something I still need to talk over
with Dag-Erling, who I am assuming is still on vacation.

- Added necessary error checking to various parts of sdiff and diff3.

Once I've tested zdiff integration in diff, I plan on sending Gabor the
latest version of BSD diff to update the port package.

I still have not completed piping to diff in diff3, but I am planning to
get diff3 functional by August 5th, which is when I will start focusing
mainly on benchmarking, checking POSIX compliance, and lots more testing.