[m-rev.] for review: add <<u and >>u as operators

[Zoltan Somogyi]

This diff modifies all three variants of the lexer.
I have bootchecked this diff while using  the string_get_token_list
and linestr_get_token_list variants, but not the original get_token_list
variant, because its much different interface makes resetting
parse_module.m to use it much more painful. However, the change to it
is small and simple enough to be checked just by eye.

We will need to note this as a breaking change, because it
breaks code that expects e.g. "<<uu" to be parsed as the tokens
"<<" and "uu", since that string will now be parsed as "<<u" and "u".
However, I would prefer to write that diff to NEWS once this diff
has been bootstrapped, and <<u and >>u have been implemented
as shifts by unsigned amounts.

Does anyone know of any other part of the reference manual
that needs to be updated for these ops?

Zoltan.
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