bug: return doesn't accept negative numbers

[Linda Walsh]

I guess I don't use negative return codes that often in shell, but
I use them as exit codes reasonably often.

'return' barfs on "return -1"...

Since return is defined to take no options, and ONLY an integer,
as the return code, it shouldn't be hard to fix.

Seem to fail on any negative number, but 'exit status' is defined
as a short int -- not an unsigned value (i.e. -1 would return 255).