add disable_cache to make_headers

Woohoo I get to add a feature! This is for #393 which we talked about on that issue. I did some research about which headers to add and what I discovered is that this is all we need to be HTTP/1.1 compatible. Things like 'pragma: no-cache' is actually HTTP/1.0 and 'expires: 1994 etc' is even earlier, I can't imagine there are many web servers that aren't 1.1 compatible at this point in the world...interestingly though the spec does say the following about pragma:

>Clients SHOULD include both header fields when a no-cache request is sent to a server not known to be HTTP/1.1 compliant. 

Meh.