If fetching clipboard times out, entry is super slow

[oberien]

Fetching the clipboard is done synchronously with a timeout of a few seconds. If no clipboard can be fetched, we have to wait for the timeout before we can enter.

[main--]

IMO #119 would be a sufficient workaround for now.

A proper long-term implementation of #23 would not have this issue anyways as we can make the Windows Clipboard API fall back to something Linux-like and have them interoperate:

• On startup: Assert clipboard ownership on Windows (delayed rendering)
• When we lose clipboard ownership on Windows (we should get a window message about that): Assert clipboard ownership on Linux
• When we lose clipboard ownership on Linux: Assert clipboard ownership on Windows (delayed rendering)
• When we receive a clipboard rendering request on Windows, we do the X11 clipboard dance (request contents, forward to VM)
• When we receive an X11 clipboard request, we grab the data from Windows (request contents from VM, forward to X11 window)

[oberien]

Fixed by #135