* iface/Makefile.am (SUBDIRS): Recurse in gspn only if condition WITH_GSPN.
* iface/Makefile.am, iface/gspn/Makefile.am: New files. * Makefile.am (SUBDIRS): Add iface. * iface/gspn/gspnlib.h: New file, from Yann and Souheib.