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.
Push through on the Meteor.connect -> DDP.connect rename.
Rename Meteor.http to HTTP. Backwards compatible.
Merge exports list with package variables in slice JSON.

This implies that all exports are package variables, which made underscore,
jquery, and htmljs (which explicitly assigned to fields on the global variable)
break. We now properly encapsulate these packages (except for window.jQuery,
which we let sneak out because bootstrap wants it).  This means that packages
that want _ need to use underscore, and packages that want $ need to use jquery.
Also, you can't use _ in minimongo $where any more (matching mongod).
oops, remove debugging code
Declare _FooTest symbols as testOnly; they are only visible to tests.

They are visible to *all* tests, not just the package's own tests.
Rename _FooTest symbols to FooTest. They are already test-only.
Mark test helpers as test-only, too.
Make backbone use the _ in its scope.
oops, define Meteor.autosubscribe correctly
Include handlebars and random in the standard app packages list.
Rename api.exportSymbol -> api.export.
Fix test failure after rebase.
Merge branch 'namespace-cleanup' into devel