Add fbd -- Faulty Block Device driver

This driver can be loaded as an overlay on top of a real block
device, and can then be used to generate block-level failures for
certain transfer requests. Specifically, a rule-based system allows
the user to introduce (overt and silent) data corruption and errors.

It exposes itself through /dev/fbd, and a file system can be mounted
on top of it. The new fbdctl(8) tool can be used to control the
driver; see ``man fbdctl'' for details. It also comes with a test
set, located in test/fbdtest.

lib/libbdev/ipc.c

@@ -38,7 +38,7 @@ static int bdev_recover(dev_t dev, int update_endpt)
   endpoint_t endpt;
   int r, nr_tries;
 
-  printf("bdev: recovering from a driver crash on major %d\n", major(dev));
+  printf("bdev: recovering from a driver restart on major %d\n", major(dev));
 
   for (nr_tries = 0; nr_tries < RECOVER_TRIES; nr_tries++) {
 	/* First update the endpoint, if necessary. */