Use only utcnow when considering dates
add workaround for if-none-match of unsafe methods

Some http libraries (I'm looking at you, iOS, but probably many others)
add if-none-match to unsafe methods even when they weren't told to.
This hack allows view code to decide it wants to violate 14.26 and
ignore the if-none-match header.
perfix all g variables with webcache_

A better solution would be to put a g.webcache object with all necessary
state/flags. But not now.
bump version