rpc.js improvements: re-re-review

[jo...@gmail.com]

Reviewers: shindig.remailer_gmail.com,

Description:
1. RMR, new transport for Safari < 4, Chrome < 2, and should work as a
backup on several other browsers (the latter claim requires more
testing).
   - Paves the way to sunsetting IFPC, in turn sunsetting the need for
containers to host "active" relay file rpc_relay.html and configure it
properly.

2. Refactoring transport code into separate "classes". This cleans up
the code a bit and makes it possible to optimize later by emitting only
the JS a given browser needs rather than JS for all techniques.

3. Early-message queueing. Makes it possible to call
gadgets.rpc.call(...) in a container to a gadget before the gadget is
initialized (or even rendered), with the call still going through when
the gadget is ready. It also ensures that G -> C calls made before G ->
C initialization is complete also succeed (this is much less prevalent).

4. Various cleanups including tentative backward-setup support. As a
convenience and to prevent user error, makes it possible to call
gadgets.rpc.setAuthToken(gadget, token); before the gadget IFRAME is
rendered. While not recommended in any case, this is intended to make
the library easier to use.

Please review this at http://codereview.appspot.com/88069

Affected files:
   features/src/main/javascript/features/rpc/fe.transport.js
   features/src/main/javascript/features/rpc/feature.xml
   features/src/main/javascript/features/rpc/ifpc.transport.js
   features/src/main/javascript/features/rpc/nix.transport.js
   features/src/main/javascript/features/rpc/rmr.transport.js
   features/src/main/javascript/features/rpc/rpc.js
   features/src/main/javascript/features/rpc/wpm.transport.js