proposed minor change to var and whatis semantics

[Noah Friedman <friedman@gnu.ai.mit.edu>]

>for var, it seems silly that ``var foo'' produces ``var is undefined''
>when the obvious ``var ='' would recreate the current (non-)value.
>
>for symmetry's sake, it makes sense that whatis does not raise an
>exception, although the underlying %whatis still has to for internal
>reasons, i think.

Both seem reasonable to me, as long as whatis says 
"foo: No such file or directory" on stderr, not stdout.