The point of doing SHA256 twice is, generally, is to prevent message
extension attacks where an attacker who knows H(A) can calculate
H(A|B).  But for attaching a signature to a document, the attacker
already _knows_ A, so trying to keep them from calculating H(A|B) is
pointless.

This means we need to handle the existence of multiple flavors of signature
in a detached signatures document, generate them correctly, and so on.

This patch introduces a new type called document_signature_t to represent the
signature of a consensus document.  Now, each consensus document can have up
to one document signature per voter per digest algorithm.  Also, each
detached-signatures document can have up to one signature per <voter,
algorithm, flavor>.

The consensus documents are not signed properly, not served, and not
exchanged yet.

The original proposal was vague and would have made older Tors reject
detached-signature documents as soon as they saw one with flavors.

Previously, we insisted that a valid signature must be a signature of
the expected digest.  Now we accept anything that starts with the
expected digest.  This lets us include another digest later.

Conflicts:
	ChangeLog
	configure.in
	contrib/tor-mingw.nsi.in
	src/or/config.c
	src/win32/orconfig.h

backport of c43859c5
backport of 0d13e0ed

Partial backport of 381766ce.
Partial backport of 56c6d785.

When we tried to use the deprecated non-threadsafe evdns
interfaces in Libevent 2 without using the also-deprecated
event_init() interface, Libevent 2 would sensibly crash, since it
has no guess where to find the Libevent library.

Here we use the evdns_base_*() functions instead if they're
present, and fake them if they aren't.

Peter Palfrader authored Oct 11, 2009 and Nick Mathewson committed Oct 11, 2009

The test suite need the test.h file to build. Add it to
noinst_HEADERS in the Makefile.am so it gets included
in the tarball that make dist produces.

Peter Palfrader authored Oct 11, 2009 and Nick Mathewson committed Oct 10, 2009

tinytest_main() returns 0 on success, -1 on errors and 1 on test
failures.  So test.c should check on !=0 instead of <0.