[pre-lexer 00/21] preparation for work on lexer

[Ben Pfaff]

I've been doing a major rewrite of the PSPP lexer (tokenizer).
It is not ready yet, but this series prepares for it by fixing
up a number of issues and making various improvements that I
have discovered along the way.

Comments are appreciated.  This is a big series, so I will give
this a week or so, unless I hear feedback back before then.

Thanks,

Ben.