Collected ABNF for HTTPbis

Hi,

I discussed generating a collected ABNF for Parts 1 through 7 with Björn 
Höhrmann (see <http://jabber.ietf.org/logs/httpbis/2009-05-16.txt> and 
<http://jabber.ietf.org/logs/httpbis/2009-05-17.txt>).

Generating it turned out to be a *bit* tricky:

- we had an unintended name collision between "parameter" in Part 1 and 
3 (fixed with <http://trac.tools.ietf.org/wg/httpbis/trac/changeset/583>)

- there are a few duplicated rules (harmless)

- some rules have a generic version in Part 1 (for instance, "Method"), 
and a more specific in Part 3; this is a known TODO

Working around the two latter issues, we can generate 
<http://greenbytes.de/tech/webdav/httpbis.abnf> which I'll keep 
up-to-date from now, for those who want to play around with it (feedback 
   appreciated).

Best regards, Julian