Make minetest abort on lua panic

Currently, lua does a regular exit() after a lua panic, which can make
a problem hard to debug. Invoking FATAL_ERROR() instead will print
some useful information, and abort() minetest, so that a debugger can
be used to analyze the situation.

src/script/cpp_api/s_base.h

@@ -118,6 +118,8 @@ protected:
 #endif
 
 private:
+	static int luaPanic(lua_State *L);
+
 	lua_State*      m_luastack;
 
 	Server*         m_server;