RFE: Allow an update to wait for another

[jasontibbitts]

If you have a package which changes frequently, or even just a couple of times close together, you run into the issue of predicting whether the a newly submitted update will interfere with an existing one.

So it would be nice to be able to file an update, but ask bodhi not to begin processing it until doing so will not interfere with another pending update.

This could be as simple as having the update submission screen list other pending updates for the same (package, fedora version) and asking if the update being submitted should override them or wait for them. And I guess the command line submission tool could gain a field to control that behavior.