Write patches for all spec-deviations in prop271

The prop271 implementation I produced is not 100% conformant to the proposal, since in some cases I found gaps or things that the proposal didn't consider. Before we merge legacy/trac#19877 (moved), we should be sure that the spec is up-to-date too.

changed milestone to %Tor: 0.3.0.x-final in legacy/trac

added component::core tor/tor in Legacy / Trac milestone::Tor: 0.3.0.x-final in Legacy / Trac owner::nickm in Legacy / Trac parent::19877 in Legacy / Trac priority::medium in Legacy / Trac resolution::fixed in Legacy / Trac review-group-13 in Legacy / Trac reviewer::asn in Legacy / Trac reviewer::chelsea in Legacy / Trac severity::normal in Legacy / Trac status::closed in Legacy / Trac tor-guard in Legacy / Trac type::defect in Legacy / Trac labels

My torspec branch, prop271-changes , has all of the changes that I (knowingly) made to the design.

Trac:
Status: new to needs_review

Trac:
Keywords: N/A deleted, tor-guard added

Trac:
Keywords: N/A deleted, review-group-13 added

Trac:
Status: needs_review to assigned
Owner: N/A to nickm

Trac:
Status: assigned to needs_review

Trac:
Reviewer: N/A to chelseakomlo, asn

spec changes look good to me. Thanks!

Trac:
Status: needs_review to merge_ready

Merged this to torspec. THank you!

Trac:
Status: merge_ready to closed
Resolution: N/A to fixed

closed

moved from legacy/trac#20834 (moved)

added Bug label and removed 1 deleted label

added Guards label and removed 1 deleted label