awk texindex switch

[Karl Berry]

I just committed changes so that the awk texindex written by Arnold will
get built and installed instead of the C texindex.  What I do for
development is make a symlink to texinfo-checkout/texindex/texindex
somewhere in PATH, so that that version will be used.  (I haven't
actually tried a make install yet.)

That texindex file is generated from texindex.in by make.  It's a small
wrapper script that execs awk on the texindex.awk script file.

This was just the first integration, I haven't done anything for make
check, among other things, as yet ...

Eli, if there are problems with this approach on Windows machines, I'd
have no way of knowing (or testing or remedying), so please let us know
if need be.

Best,
Karl