Comprehensive namespace cleanup.
Clean up namespacing in accounts system too.
- drop `where` from all on_use/on_test (it is no longer being passed in)
- allow `api.use(package, {options})` without where
- fix showdown to use a weak dependency
Drop all @export lines. Add api.exportSymbol instead.
first stab at dropping the @export comment parser
update awssum
test-packages now has no immediate server-side errors (client-side, sure)

eliminate accounts-urls package
most tests pass, just not coffeescript
fix coffeescript.  test-packages passes!
Get rid of linkerFileTransform.
move email's hookSend onto _EmailTest
rename logging test that is no longer in logging
clean up server/client_convenience
preserve the existence of Meteor._Mongo
fix accounts package detection to work again
Don't interact with Reload for server-to-server DDP.
Make audit-argument-checks into an empty package, detected via weak deps.

This requires making sure that empty packages work!
Make insecure into an empty package, detected via weak deps.
Make autopublish into an empty package, detected via weak deps.
Eliminate the "past" package.

This package was always included in apps, and even if it was possible to remove,
there wasn't a compelling story about when users would remove and replace
it. Plus, not all backwards-compatibility code could even live in it (eg, field
names of objects), so it was incomplete. It also introduced odd load order
constraints.

Instead, we introduce two conventions for backwards-compatibility code:

  - Special comments of the form "// XXX COMPAT WITH 0.6.4"
  - When feasible, put backwards-compatibility code in a file called
    "deprecated.js" in the relevant package.

This is documented at:
https://github.com/meteor/meteor/wiki/Meteor-Style-Guide#deprecated-code-and-backwards-compatibility

Additionally, removed some symbols that existed for backwards compatibility with
Meteor 0.4.0 (changes made 10 months ago): Meteor.is_client, Meteor.is_server,
and (in a method) this.is_simulation.