fastcgi egg segfaults with SIGUSR1

[bcaine]

libfcgi has the option to gracefully terminate in response to SIGUSR1.

The fastcgi egg doesn't properly detect this case and segfaults. When it's shutting down, the FCGX_Request's out field (and probably all the fields) go to null.

This patch to fastcgi.scm fixes it:

245c245,246
<       (and-let* (((callback
---
>       (and-let* ((_ (fcgi-request-out req))
>                  ((callback

The fastcgi egg is very old and the original author doesn't maintain it anymore. I would appreciate it if someone could apply this patch.