Extract the action scanner from the grammar scanner

[Akim Demaille]

I have already referred to this change several times.  Our current
scanner is very complex and has subtle interactions with our parser.
This is hard to maintain, and also prevents easy extensions of
our grammar (which defeats the whole point of having moved to
using bison for Bison).

I was about to install this patch when I read Paul's message about
2.3 being out soon?

split-scan-gram.txt
Description: Text document