Convention plugin recap - proposal

[musachy]

On our super long convention thread, we got to the agreement that in order  
to move convention out of the sandbox, there should be a way to run both  
plugins side by side, so backward compatibility could be possible. The  
remaining issue to make that happen was to implement "multiple unknown  
handler", for which I uploaded a new patch here (against trunk):

http://jira.opensymphony.com/browse/XW-640  
(http://fisheye6.atlassian.com/cru/DEMO-19)

that creates an extension point for unknown handlers manager, instead of  
some ugly static classes I wrote before. We also agreed to include  
convention after 2.1 was released, but based on how long releases  
take(hoping to change that soon), I propose that we move convention out of  
trunk for the next 2.1 release so it will be available when 2.1 goes GA,  
and not 1 or 2 years after that.

@Rainer, @Rene: could you guys take a look at the new patch? That thing was  
a pain to merge being so old, the new one should merge fine.

regards
musachy