This invention relates to the use of a compound of formula ##STR1## wherein X is --CH.sub.2 -- or ##STR2## R.sub.1 is H, C.sub.1-5 -alkyl or benzyl, which can be substituted of unsubstituted; R.sub.2 is H, C.sub.1-4 -alkyl, C.sub.1-4 -alkenyl, OH, or C.sub.1-3 -alkoxy; R.sub.
