Fix for negative and zero values for loop iterations.

Small fix for line counter so we don't get POP when L takes us to the
end of the buffer.
Add illegal commands.
Add support for ^U.

Fix silly typo.
Update comments.
Commit before 'expand'.
Expanded all tabs to spaces.
Fix to skpset() so that it correctly skips loops.  See test 001.tec
for the regression test.

This fixes #1.
Regression test for issue #1.  Not sure exactly how these tests will be
run or controlled.  However, it is just important that they are added in
at this point.