Do garbage collection on luacore

Another lua state that is not freed until end of game,
so clean up the stack and do GC regularly.

src/nhlua.c

@@ -174,6 +174,7 @@ l_nhcore_call(int callidx)
           nhcore_call_names[callidx]);*/
         nhcore_call_available[callidx] = FALSE;
     }
+    lua_settop(gl.luacore, 0);
 }
 
 DISABLE_WARNING_UNREACHABLE_CODE
@@ -1115,6 +1116,7 @@ nhl_variable(lua_State *L)
     lua_getglobal(gl.luacore, "nh_lua_variables");
     if (!lua_istable(gl.luacore, -1)) {
         impossible("nh_lua_variables is not a lua table");
+        lua_settop(gl.luacore, 0);
         return 0;
     }
 
@@ -1139,6 +1141,7 @@ nhl_variable(lua_State *L)
             nhl_pcall_handle(L, 0, 1, "nhl_variable-1", NHLpa_panic);
         } else
             nhl_error(L, "Cannot get variable of that type");
+        lua_settop(gl.luacore, 0);
         return 1;
     } else if (argc == 2) {
         /* set nh_lua_variables[key] = value;
@@ -1168,6 +1171,7 @@ nhl_variable(lua_State *L)
             nhl_pcall_handle(gl.luacore, 0, 0, "nhl_variable-3", NHLpa_panic);
         } else
             nhl_error(L, "Cannot set variable of that type");
+        lua_settop(gl.luacore, 0);
         return 0;
     } else
         nhl_error(L, "Wrong number of arguments");
@@ -1189,6 +1193,7 @@ get_nh_lua_variables(void)
     lua_getglobal(gl.luacore, "nh_lua_variables");
     if (!lua_istable(gl.luacore, -1)) {
         impossible("nh_lua_variables is not a lua table");
+        lua_settop(gl.luacore, 0);
         return key;
     }
 
@@ -1196,10 +1201,12 @@ get_nh_lua_variables(void)
     if (lua_type(gl.luacore, -1) == LUA_TFUNCTION) {
         if (nhl_pcall_handle(gl.luacore, 0, 1, "get_nh_lua_variables",
                              NHLpa_impossible)) {
+            lua_settop(gl.luacore, 0);
             return key;
         }
         key = dupstr(lua_tostring(gl.luacore, -1));
     }
+    lua_settop(gl.luacore, 0);
     return key;
 }
 
@@ -1237,6 +1244,7 @@ restore_luadata(NHFILE *nhfp)
     luaL_loadstring(gl.luacore, lua_data);
     free(lua_data);
     nhl_pcall_handle(gl.luacore, 0, 0, "restore_luadata", NHLpa_panic);
+    lua_settop(gl.luacore, 0);
 }
 
 /* local stairs = stairways(); */
@@ -1552,6 +1560,7 @@ nhl_callback(lua_State *L)
         lua_pushstring(gl.luacore, cb);
         lua_pushstring(gl.luacore, fn);
         nhl_pcall_handle(gl.luacore, 2, 0, "nhl_callback", NHLpa_panic);
+        lua_settop(gl.luacore, 0);
     }
     return 0;
 }
@@ -1951,6 +1960,8 @@ nhl_pcall_handle(lua_State *L, int nargs, int nresults, const char *name,
                        lua_tostring(L, -1));
         }
     }
+    if (L == gl.luacore)
+        lua_gc(L, LUA_GCCOLLECT);
     return rv;
 }