Add replaceEntry method to AccessControlUtil?

[Ray Davis]

I happened to be looking at the ModifyAceServlet issue described at 
SLING-997 late last week and noticed almost exactly the same logic 
(except without the bug) in 
jcr/contentloader/internal/DefaultContentCreator. In the Sakai 3 
project, Ian added a utility method to consolidate the same rather 
complex logic of replacing access controls for a specific Principal on a 
specific path, and it's proven very popular among service developers.

I'd like to try submitting a similar utility method to Sling, but wanted 
to check with the development team first in case there's a conflict with 
other near-term authz tasks.

Thanks,
Ray