[PATCH 0 of 2] cache fixes for empty and stale responses

[Maxim Dounin]

Hello!

Here are patches to fix two known problems with cache, see here for more
information:

http://nginx.org/pipermail/nginx/2009-October/015789.html
http://nginx.org/pipermail/nginx/2009-December/017792.html

Patch for empty responses was rewritten to more closely match static module
instead of diverging from it.

Patch for stale responses was separated and fixed not to break builds without
http cache.

Maxim Dounin