how to speedup the build process of our web pages

Hi,

I've patched cron/parts/7release-notes and added some code, that
checks if there were some changes to the release-notes repository.
If not, don't rebuild the release-notes. Details:
git show 4560761a19d830e..d7864a901a552a18d

In the past this part took nearly 90 minutes on www-master, six times
a day. But the last change was mid of July. If we expect no changes
until end of this year, we will save 800 hours of build time.

Next target could be cron/parts/4webwml. Does anyone knows if there is
a reason why we do not use a parallel make, using all 4 cores of
www-master?