Bug: Call hook may be called twice when count hook yields

Took the opportunity and moved the code that controls call hooks
in 'luaV_execute' into a function.

ldebug.h

@@ -58,6 +58,7 @@ LUAI_FUNC const char *luaG_addinfo (lua_State *L, const char *msg,
                                                   TString *src, int line);
 LUAI_FUNC l_noret luaG_errormsg (lua_State *L);
 LUAI_FUNC int luaG_traceexec (lua_State *L, const Instruction *pc);
+LUAI_FUNC int luaG_tracecall (lua_State *L);
 
 
 #endif