Update server support; remove libcurvecpr-glib.

This changeset backports changes to the libcurvecpr core library from
the add-glib-server branch. It further removes libcurvecpr-glib entirely
from the source tree; the GLib-based source code will be made available
in a separate repository (currently
https://github.com/impl/libcurvecpr-glib).