Menu callback improvements

[tstanley]

I have noticed that there are some tricks that can be played with Control and Panel callbacks that cannot be done with Menu callbacks.  More specifically, it would be handy at times to be able to chain menu callbacks, and to be able to programmically call menu callbacks given the menubar/menuitem ID.  Specifically I am looking for new library functions along the lines of CallMenuCallback(), ChainMenuCallback(), UnchainMenuCallback(), etc.

Thanks. 

[ElectroLund]

I second this!  I'm surprised there's still no way to chain a callback onto a menu item.