support for making sure exceptions are reset when they should be reset (obs from Nuno Fonseca, #159)

C/exec.c

@@ -1587,7 +1587,7 @@ Yap_InitYaamRegs(void)
   Yap_regp = &Yap_standard_regs;
 #endif
 #endif /* PUSH_REGS */
-  Yap_DeleteGlobal (AtomCatch);
+  Yap_ResetExceptionTerm ();
   Yap_PutValue (AtomBreak, MkIntTerm (0));
   TR = (tr_fr_ptr)Yap_TrailBase;
   if (Yap_AttsSize > (Yap_LocalBase-Yap_GlobalBase)/8)
@@ -1728,6 +1728,13 @@ p_reset_exception(void)
   return Yap_unify(t, ARG1);
 }
 
+void
+Yap_ResetExceptionTerm(void)
+{
+  Yap_ReleaseTermFromDB(BallTerm);
+  BallTerm = NULL;
+}
+
 static Int
 p_get_exception(void)
 {