tweak handling of slow/missing upstream

our fetch and render timeouts were both 20s,
causing the 'finish early' event to fire immediately before 
the upstream timeout turns it into a 400.

This moves the upstream connection timeout to 10s,
meaning unavailable servers will hit 400 instead of 'working...'.

I also removed the 'Fetched...' timing diagnostic message when the fetch fails.
Merge pull request #243 from minrk/slow-fetch

tweak handling of slow/missing upstream