bug#60711: Compose fails to generate ≤ and ≥ (only those two! and only in emacs!)

[Gregory Heytings]

> The compose key requires either compose state to be kept by the program 
> in cooperation with XLookupString, or is implemented by the input 
> method.

You're right.  I thought this was happening entirely inside Xlib, and 
indeed it requires some cooperation of the program.  It seems that this 
cooperation is minimal, though: IIUC, the client should just immediately 
discard the events when XFilterEvent returns True, that is, until the 
composed character is delivered.