and this prevented users from implementing "purge on POST" semantics
by looking up the POST requests and ditching the object found.

Now we only overwrite the request with "GET" if it is a HEAD, (the
internal "wantbody" flag tells hos how the response should be composed.)

The testcase shold probably be elevated to VCL example, with suitable
footnotes about URL sanitizing etc.

Fixes #444



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@4042 d4fa192b-c00b-0410-8231-f00ffab90ce4