[MERGE] Fix PreviewTree.annotate

[John Arbash Meinel]

John Arbash Meinel has voted tweak.
Status is now: Conditionally approved
Comment:
Just layering a annotate.reannotate() on top of extracting the text IFF 
the text should have changed. Seems good.

Though you don't test annotate_iter() when there are no changes. I would 
like you to, just to exercise more code paths.

And maybe also if you change something which *isn't* a content change. 
Like maybe renaming the file?
Basically, I would like to make sure that each branch in the code is at 
least passed over. (Helps to find typos, etc.)

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C4863F421.3050401%40aaronbentley.com%3E