check for compatible LAMMPS version when creating LAMMPS instance

This check must be done at runtime, since the LAMMPS shared library
may have been loaded dynamically and thus required library functions
may not be present or missing features with too only a LAMMPS version.

tools/lammps-gui/lammpswrapper.h

@@ -29,6 +29,7 @@ public:
 
     void force_timeout();
 
+    int version();
     int extract_setting(const char *keyword);
     void *extract_global(const char *keyword);
     void *extract_atom(const char *keyword);