Hello Jeremy,

  JCR> Maybe you need the glib2 installed also.

I already had both glib and glib2 installed (it was lazy of
me not to post "pkg_info|grep glib" output).  I was confused
by the error message's use of GLIB and Glib, since I know
pkgsrc tends to use lower case.  I forced an uninstall of
glib2 and rebuilt it, and eventually got xplanet installed.
Now I just have to remember how to make it display satellite
ground tracks :-)

Thanks,
  - Andy Ball