generalize the "test something in an iframe" code in unit tests

[mikesherov]

there are 3 different pieces of code in 3 different unit test modules:

support.js: supportIFrameTest
selector.js: testIframe
offset.js: testoffset

testIframe and testOffset are almost exact duplicates. supportIFrameTest is close enough. I was about to start writing another one for a ticket I'm trying to fix in event.js, but perhaps it's time to DRY this code and move it into test/data/testinit.js ?

I'd be glad to take a stab at it. 1.8?

[dmethvin]

Sounds like a good idea!