extend dojo.io.script to allow attaching to child iframes

[jburke]

For comet long polling using script tags, Firefox and Opera operate attached scripts in DOM order, and not network order. This means a long-polling script tag can block other attached scripts.

Allow for a way to tell dojo.io.script to attach and get callbacks from a child iframe, to allow attaching long polling scripts in the iframe. This will free up the main window to do other script attachments without being blocked.

[jburke]

(In [12851]) Refs #6064. Allow dojo.io.script to use a child iframe. This gets the basics in there, and leaves the higher order issues of setting up the iframe to the user. Still need to document it. Ideally also show an example, but that might take longer.

[jburke]

Pushing this to 1.2 for the more complete example, maybe a dojox.io module to handle this. For now the basic enabling layer is in.

[jburke]

(In [14235]) Refs #6064: get script removing working with frameDoc, and also fixes a multiversion bug with a 'dojo' string reference.

[jburke]

(In [14236]) Fixes #6064: provides dojox.io.scriptFrame for running long-polling script tags in an iframe.