[MERGE] Allow plugins to select test runner class

[Andrew Bennetts]

Andrew Bennetts has voted tweak.
Status is now: Conditionally approved
Comment:
PEP 8: there needs to be a space after colons in dict literals.  If you 
don't like that use the dict(x=x) syntax ;)

I think we'll find that providing a runner registry will be a nicer UI 
for plugin authors... I'd be interested to hear jml's thoughts regarding 
using this for running bzr tests with Tribunal.  But this patch doesn't 
really make bzr itself ugly (even if the code in plugins to take 
advantage of it will be ugly), so I don't object to merging it.  My gut 
feeling is that sooner or later we will want make this easier for 
plugins, though.



For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C1234415066.12070.648.camel%40lifeless-64%3E
Project: Bazaar