Lexer again.

Sorry, guys. Here is the ultimate patch which keeps the entire
behavior as it was, apart from forbidding minus-terminated 
operators. Seems that I have to break the habit of doing before
thinking properly :-/  The point is that my second patch breaks
constructs like a & b  or   a ! b. This patch is to be applied 
instead of any of two other today's patches.

-- 
Leon.