HTTP client fetch timeouts, let spidering finish.

In addition to "operation timed out", there's some state where a TCP
connection can be established but we never, after days, get a response.
It might be tarpitting.  I don't know or care: instead, the client fetch
now wraps the fetch with a timeout, leading to:

    2013/01/20 05:37:53 spider.go:337: Failure fetching "[censored]": HTTP Do() timed out after 2m0s

Fixes issue #3