Do not execute unnecessary transmissions

Originally reported on Google Code with ID 191

```
When several bundled transmissions affect the same pane, we should somehow only draw
the pane 
once.

Perhaps we could have some sort of a signal when the complete round of transmissions
have 
finished, and only trigger the rendering of the presentations afterwards.
```

Reported by `tudor.girba` on 2009-10-20 22:42:56
