Fixed select bug in devel

The select system got broken in the last round of devel changes.  The patch
is very minor:

$ hg diff
diff -r 9f6b8596d82b c/unix/event.c
--- a/c/unix/event.c	Fri Jun 27 08:35:39 2008 +0200
+++ b/c/unix/event.c	Mon Jun 30 17:23:11 2008 -0700
@@ -841,7 +841,7 @@
       return errno;
   }
 }
-#elif defined HAVE_SIGNAL
+#elif defined HAVE_SELECT
 /*
  * Call select() on the pending ports and move any ready ones to the ready
  * queue.  If wait is true, seconds is either -1 (wait forever) or the