In case of <changeowner> only UID and GID were changed, 
supplementary groups were left in place.
This is a potential security issue only if <changeowner> is used.
New behaviour is to set UID, GID and set supplementary groups 
based on the UID
Even in case of icecast remaining in supplementary group 0 
this "only" gives it things like access to files that are owned 
by group 0 and according to their umask. This is obviously bad,
but not as bad as UID 0 with all its other special rights.
It's a security issue and we fix immediately and recommend users to update.

PS: Cherry picking this should be fine by distros for fixing older releases.

svn path=/icecast/trunk/icecast/; revision=19137