uploadProgressBlock is not called when using STTwitterOS

Hi,

I found this issue while using STTwitter with iOS and ACAcount.
The uploadProgressBlock I provided to ```[STTwitterAPO postStatusUpdate: ...]``` was not called.

STTwitterOS is ignoring it. I found a comment ("ignored") next to block which surprise me because it seems to be on purpose. I checked history and I couldn't find the reason.

I tried this fix and it works.

Thanks,
Ariel