Mozilla2:Misc changes

This page lists smallish changes that should be done once we can break compatibility.

- Make necko's status codes be non-overlapping with error codes (nsITransport, nsISocketTransport)

- Remove some of the string types in IDL (string, wstring, and perhaps ACString)

- Improve our input stream situation. Ideally: Kill nsIScriptableInputStream, kill nsIBinaryInputStream, make nsIInputStream scriptable