[MERGE][1.14] simplify the content filter registration API

[Ian Clatworthy]

John suggested this on IRC and Jelmer has agreed it's a good idea.
We want this cherrypicked into 1.14 so that the API for plugins is
stable going forward.

Ian C.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: register-filter-api-tweak.patch
Type: text/x-diff
Size: 7117 bytes
Desc: not available
Url : https://lists.ubuntu.com/archives/bazaar/attachments/20090406/11b3486e/attachment.bin