Fix for #2175 - Spacebars block comment cause unexpected errors

This fixes an edge case where a comment is followed immediately
by an {{else}} token.
Merge pull request #2180 from arbesfeld/comments-fix

Fix for #2175 - Spacebars block comment causes unexpected errors
Fix #2157 (issues with `=` in template args)
Add _nestInCurrentComputation flag to UI.render.

Internally, Blaze sometimes relies on `UI.render`'s autoruns nesting
within the current computation, but it's often the case that callers
don't want `UI.render`'s autoruns to be stopped when the outer
computation is invalidated. This change fixes a bug in {{#each}}: if
`addedAt` ran inside a `Deps.autorun`, and then the outer computation
was invalidated, the corresponding item would stop updating because the
autoruns set up by `UI.render` would be stopped.

Fixes #2156.
Use Meteor.absoluteUrl() to redirect in force-ssl
Expose underscored animation hooks and add a test
Update an accounts-ui-unstyled comment
Show name of logged-in user after email verification/password reset
Merge branch 'login-display-username' into devel
Rename `closePopup` to `OAuth._endOfLoginResponse`.
Nick's comments
Remove dead ?redirect OAuth flow.

This code has never worked without some fairly serious client-side
surgery, and it now especially doesn't work because it doesn't
communicate the credentialSecret back to the app. Rather than leave an
untested, unQA-ed code path in core, apps that are using the ?redirect
flow can just override `OAuth._endOfLoginResponse` to do the redirect
themselves.
Change _endOfLoginResponse signature.

The main changes are:
* The `isSafe` check happens before _endOfLoginResponse is called. If
  _endOfLoginResponse gets a credential token/secret, then the values
  are safe to include in HTML.
* _endOfLoginResponse gets a little more information about the request
  (like the query string, and a string or Error describing any error
  that occurred).
* We preserve the <=0.8.1.3 behavior where you have to pass ?close in
  the query parameter to get the popup to be closed at the end of the
  OAuth flow.