properties are still missing.

* iface/dve2/dve2.cc, iface/dve2/dve2.hh: Add
classes for presenting the DiVinE2 model as a kripke object.
(load_dve2): Load the *.dve2C file using libltdl.
* iface/dve2/Makefile.am: Add a dve2check program.
* iface/dve2/dve2check.cc: New file.  Currently it just
outputs the reachability graph using dotty.