Split diagnostics into errors and warnings.  Warnings are
issued when the intent is clear and we can carry it out,
everything else is an error.

Collapse tag/endtag procssing, it's simpler.

Various code cleanups.




git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5750 d4fa192b-c00b-0410-8231-f00ffab90ce4