Rework exception-handling code for current feedparser.

Rework exception-handling code for current feedparser.

Errors from urllib2 used to be reported in bozo_exception. They are now
raised directly from feedparser.parse, which probably makes more sense.
rawdog now handles both cases, putting network-ish exceptions into
rawdog_exception either way; it also sets rawdog_timeout when a timeout
occurs, which should make it easier for plugins to detect this.

As a result, there's no longer a distinction between the "Error while
fetching feed" and "Error fetching or parsing feed" messages, and a
traceback can be printed for both if showtracebacks is on.