fix copy and paste in the same tpt window on SDL/Linux/X11

Explanation:
When it was pulling from itself, X11 sent TPT an event, but the tiny event storing loop simply stored it without handling
I moved all event processing to an external EventProcess (forward-declared) so that i can call it from other places too,
Also i added XA_UTF8_STRING to list of supported atoms (it only exported XA_STRING, but requested a XA_UTF8_STRING),
Also i fixed a case where pasting yields no data, or when it is unsuccessful.
Also i removed the micro event loop inside the ClipboardPull, and am calling fullblown EventProcess