Remove cursor.rewind interface

Our cursor interface has no nextObject method, so there's no point in
having a rewind method. Its major effect is ensuring that
fetch/forEach/map return no documents if you've already called one of
them once. It's not clear why this is actually useful to anybody.

rewind is kept around as a no-op; if we later implement nextObject, we
can make rewind do something, but we still presumably would auto-rewind
before fetch/forEach/map.

In minimongo, remove the db_objects cache inside each cursor. The only
actual use of this cache was that if you called count multiple times, it
would return the same number without re-running the query, and you could
share the query work between N calls to count and one call to
fetch/forEach/map (but only one call! future calls would return
nothing!)  While there's a minor performance hit from getting rid of
this cache, it should also use a little less memory, and enable use
cases like

   {{#with someCursor}}
     {{#if count}}
        {{#each this}}
          ...
        {{/each}}
     {{/if}}
   {{/with}}

which didn't work before because even the deps invalidation didn't
rewind the cursor.

Also, as a minor optimization, skip an EJSON.clone if there's a
projection, because projection functions are guaranteed to clone.

Fixes #2114
Only do one query for forEach/count in Deps

They used to run the query twice: once for the actual result and once to
set up the observe. Now it shares the work between the observe and the
actual query.

This required me to inline the _depend helper, but I actually think this
made what's going on more direct and clear.

Drop the _allow_unordered hack. I'm not convinced that it was ever truly
valid; the observe code really doesn't support unordered observes with
skip and limit, and I could not remember what it was about count's use
that made it hypothetically safe.  Easier to just remove the hack (until
we maybe eventually actually fix #1643)

Stop using Deps.Dependency in an unidiomatic way; just use
Deps.currentComputation directly.
Remove a dead import
Stop not updating form controls if they're focused

On Blaze, we copied functionality we had on Spark: Don't update
form controls (INPUT, TEXTAREA) if they are focused and their underlying
value reactively updates. This was never meant to be the eventual
solution -- we'd eventually have a way to define strategies for two-way
data binding. Maybe you'd be able to define a callback that notifies
the app when a change happens to a field that hasn't been saved yet.

Moreover, not only is the feature incomplete, but with Blaze it works
much more poorly than in Spark. Due to fine-grained updates, users
his this more frequently and don't seem to like the behavior
(in Spark you would only hit this behavior if you set up your
preserve rules exactly right, which many users did not do).

So, we're just ripping out this functionality. Now if a field gets
edited by some other user while you're focused it will just lose its
value. Focus will remain.

Fixes #1965
Make UI._templateInstance throw when not in helper.
Tweak UI._templateInstance error message
Updated deploy-examples.sh script for Rainforest QA runs
Minor changes on deploy-example.sh
Configure parties oauth in deploy-examples
Check for localStorage, catching exceptions - fixes #1291, fixes #1688.

Accessing `window.localStorage` can immediately throw an exception, which needs to be caught.
For more information, see http://www.w3.org/TR/webstorage/#dom-localstorage.
Fix ui hooks tests on IE
Make sure autoruns for {{#with}} get cleaned up.

Related to #2145, #2023, #2031.
Migrate from SRP to bcrypt.

See the spec https://meteor.hackpad.com/SRP-bcrypt-J5mdBojeVfe for
details.
account data is no longer used for the srp challenge
code review items
code review II
Nick code review items (mostly comments)
Make an error message nicer
Remove 'plaintextPassword'.

'password' can always be either a string or an object (indicating that
it's been hashed already with something). When the server receives a
string, it hashes it with SHA256 before bcrypt.