store MD5 keys

I just want to run something past the list:

Currently store MD5 keys include the request method in the MD5
calculation.

I think this is wrong. We end up having to build a fall-back list of
what methods produce replies we can cache, AND having to iterate through
all possible methods to fully flush a URL's reference.

I.e. when we see a PUT we are meant to make all variants of that entity
stale.

So, for 2.6 I'd like to remove the method from the store key
calculations, allowing much simpler logic for some of the HTTP MUST
clauses.

This cropped up when I allowed HEAD requests through the cache, and a
HEAD response arrives that is more recent that the object we are
validating. The GET request gets ejected, leaving only the HEAD request
behind. Not great. I can deal with this as a special case but I'd rather
see the core problem solved.

We will need the method available for client side processing, and a list
of the all the variants of the object... but an extension of the under
development ETag logic to track the method as well as the MD5 should
handle that.

Thoughts?

Rob