this saves about 1 millisecond for each URL reference, which has some good effect
on the search result computation if a word is searched that appears very often
(speed-up of 1 second and more)
git-svn-id: https://svn.berlios.de/svnroot/repos/yacy/trunk@4033 6c8d7289-2bf4-0310-a012-ef5d649a1542