Revert "Misc fixes."

This reverts commit 32f6477cdc3fb13ff98f33181cfdcc1a190a8fb1.
Portability fixes.
Silence some misterminated file warnings.
Use the officially-sanctioned method to invalidate a GTK+ window from any thread.
Fix omission of request callback, which was causing null ptr to be returned.
Need to choose a windows version to get threading support.