Prototype and implementation of jdata::get_nj_max.

Essential is the '#ifdef GPU', since, when one executes "./setup install amuse-ph4" one will not link with Sapporo as one would when executing "./setup install amuse-ph4-sapporo".
So "GPU" and "Sapporo" go hand in hand and one needs to make sure that "./setup install amuse-ph4" will complete without error when no GPU is available.

Author: HannoSpreeuw

src/amuse_ph4/src/jdata.cc

@@ -34,6 +34,7 @@
 
 #ifdef GPU
 #include "grape.h"
+#include "sapporo.h"
 #endif
 
 // AMUSE STOPPING CONDITIONS SUPPORT
@@ -1153,3 +1154,12 @@ real jdata::get_tnext()
     int ndum;
     return sched->get_list(NULL, ndum);
 }
+
+int jdata::get_nj_max()
+{
+#ifdef GPU
+    return g6_get_nj_max_();
+#else
+    return 0;
+#endif
+}

src/amuse_ph4/src/jdata.h

@@ -212,6 +212,7 @@ class jdata {
     void spec_output(const char *s = NULL);
     void to_com();
     real get_tnext();
+    int get_nj_max();
 
     // In gpu.cc: