Add emulator_ready() lua function

This function gives a flag telling if emulator has finished booting
up.

include/core/lua-int.hpp

@@ -14,6 +14,7 @@ bool get_boolean_argument(lua_State* LS, unsigned argindex, const char* fname);
 void push_keygroup_parameters(lua_State* LS, const struct keygroup::parameters& p);
 extern lua_render_context* lua_render_ctx;
 extern controller_frame* lua_input_controllerdata;
+extern bool lua_booted_flag;
 
 template<typename T>
 T get_numeric_argument(lua_State* LS, unsigned argindex, const char* fname)

src/core/lua.cpp

@@ -196,6 +196,7 @@ void push_keygroup_parameters(lua_State* LS, const struct keygroup::parameters&
 
 lua_render_context* lua_render_ctx = NULL;
 controller_frame* lua_input_controllerdata = NULL;
+bool lua_booted_flag = false;
 
 namespace
 {
@@ -420,6 +421,7 @@ void lua_callback_do_readwrite() throw()
 
 void lua_callback_startup() throw()
 {
+	lua_booted_flag = true;
 	if(!callback_exists("on_startup"))
 		return;
 	run_lua_cb(0);

src/lua/core.cpp

@@ -45,4 +45,9 @@ namespace
 		command::invokeC(text);
 		return 0;
 	});
+
+	function_ptr_luafun lua_booted("emulator_ready", [](lua_State* LS, const std::string& fname) -> int {
+		lua_pushboolean(LS, lua_booted_flag ? 1 : 0);
+		return 1;
+	});
 }