Bisect plugin updated

[Jeff Licquia]

Robert Collins wrote:
> I think it would be good to add some queryable metadata to plugins for
> building a registry of them. To be able to process this with the plugin
> uninstalled and missing dependencies is desirable (so that you can index
> a plugin you /can't/ load (such as one for windows only). So I propose
> some variables put in setup.py as globals - you can import setup.py and
> query it. And setup.py is the only thing guaranteed importable :). If
> someone has a buggy setup.py (e.g. one that forgets to do 
> if __name__ == 'main':
>    setup stuff here
> 
> Then we can file bugs :).

I've run with this.  Your system should be in bisect now, with some 
additions.

> I propose the following variables:
> The name the plugin expects to be installed under:
> bzr_plugin_name = 'bisect'

I've added "bzr_plugin_version", "bzr_minimum_version", and 
"bzr_maximum_version".  The plugin version should be self-explanatory; 
minimum and maximum versions refer to the version of bzr the plugin 
supports, for those plugins that want to do this.  Either or both can be 
"None".

Comments?  In particular, I like the idea of exposing dependencies on 
bzr versions, but am not entirely satisfied with the implementation.