- fix build for SLE 15: buildrequire also Xdamage
- make more clear when xmms2 support is compiled in
- use pkgconfig()-style buildrequires for X libraries, package
is build for suse_version >= 1315, so they are defined
- fix 0%{is_opensuse} to 0%{?is_opensuse} on one placeand remove
is_opensuse definition, which is in my opinion useless afterwards