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.

common/include/sys/Makefile.inc

@@ -3,7 +3,7 @@
 .PATH: ${MINIXSRCDIR}/common/include/sys
 
 INCS+= 	elf32.h elf64.h elf_common.h elf_generic.h \
-	ioc_block.h ioc_file.h ioc_tape.h ioc_disk.h \
+	ioc_block.h ioc_fbd.h ioc_file.h ioc_tape.h ioc_disk.h \
 	ioc_memory.h ioc_sound.h ioc_tty.h \
 	kbdio.h mtio.h svrctl.h video.h vm.h procfs.h elf_core.h exec_elf.h