It was tracking the Tor client's notion of the consensus, in a poor way. It
now can do one or the other, depending on constructor option.

Also, add some APIs that are helpful for torperf.

Oops - apparently I used a Python 2.5ism in trying to remove a
Python 2.5ism :)

Commit 33bf5a0a4a9 broke python 2.4 compat by using string.partition(),
introduced in Python 2.5.  Use string.split() instead.

Now that copyright infringement is the #1 priority of the FBI,
we need to stop doing quite so much of it.

Need to escape the dot character to get the intended
behavior.

By only running one regular expression per descriptor line and
performing a slightly better way of checking which line type
we're handling, we cut the run time of build_from_desc in half.

Allow callers to handle a specific status code as an integer as well as
the associated message within an ErrorReply exception.  Should be API-compatible
as the associated keyword arguments are popped from the **kwarg dict before
being passed to the parent exception class.

If an unknown exception is raised on one NS document during
read_routers, it's very likely it's going to be raised again on the
next, and the next... (e.g., TorCtlClosed).

Instead of printing out the traceback and continuing, allow it to
unwind the stack and let the caller handle it.