Now that hudson has some sophisticated code metric plugins it would be
particularly useful to be able to know the history of these metrics.

In a CI environment, the builds tend to run very often and thus lots of space
is required to store even 3 months worth of build history.

For that reason for instance, the starting value of the checkstyle violations is
lost. I only know the very recent history.

It would thus be very useful to be able to specify that after the "days to
keep/number of build to keep", keep every X number of builds. Value
configurable. That way I track my metrics over the life of the project and I can
tell the relevant people, look what we've done with our code metrics.

It would also allow me to track number of tests over time.

A conditional on the "keep build for ever" activity that executes this every X
times would achieve this.