Delay as long as possible before calling OpenClipboard(),
call CloseClipboard() as quickly as possible after that.
Don't call OpenClipboard() when we don't need to (for example,
we don't need to open clipboard to call GetClipboardOwner()).
Also, print out actual W32 error code in some cases where it
was not printed before.
https://bugzilla.gnome.org/show_bug.cgi?id=763907