clfilter: use filtering in `visibleheads`...
clfilter: use filtering in `visibleheads`
This is the second real use of changelog filtering. The change is very small to
allow testing the new filter with a setup close to the original one.
We replace custom post processing on `heads`function by call to the standard
code pass on a filtering repo.
In later coming will have wider usage of filtering that will make the dedicated
function useless.
