on Qt version 5 now; for those who are not comfortable with upgrading to the
new version of Qt, `astro/stellarium-qt4' port is available, serving version
0.12.4. Add an UPDATING entry to alert users about this.
While here, make scripting support optional in `astro/stellarium-qt4', since
it allows to use one less dependency. Unfortunately, this is not applicable
to 0.13.0 as required `x11-toolkits/qt5-declarative' port has USE_QT5=script
unconditionally.
Relax USE_GL knob for both ports: only libGL itself is required, not libGLU.
