WIP, try to some changes w/o diff (but gluing code is there)
WIP maybe spotted a bug

There are two versions of code:

- commented out pieces
- active pieces

Commented out pieces use format of {id: doc._id, item: doc}.

Active code uses just doc and relies on _id.

When running with old code, tests fail and 'failedTests' template prints the
names of tests, those failed in test-in-browser mode.

When running with new code, tests fail and 'failedTests' template prints [object
Object] instead of actual strings. Inspection shows that the return value of
helper 'failedTests' actually returns an array of strings. Weird.

Show to Avital tomorrow...
Things started to work kinda, tests fail, lots of logs.
Remove logs
Implement correct set of callbacks with transitions from null|array|cursor to null|array|cursor
Add correct tests, adjust to implementations details (changed is called to everything that survived the transition)
More comments
Revert changes to minimongo
Don't diff not EJSONable things
Avital's comments
Merge branch 'shark-observe' into shark

Optimization for the observe-sequence.