VFS: unbreak select on /dev/tty

The remapping from /dev/tty to the real controlling terminal in the
device code was confusing the select code.  The latter is now aware
of this case and should handle it properly, at the cost of one extra
field in the filp structure.

There is a nasty, hopefully sufficiently rare case of /dev/tty being
kept open while controlling terminals are changing, that we are still
not handling.  Doing so would require more than just a few changes,
but the code should at least detect and cleanly fail on this case.

Test77 now has a basic test set for selecting on /dev/tty.

Change-Id: Iaedea449cdb728d0e66a9de8faacdfd9638dfe92
some small changes

	. add /sbin to tests $PATH for ping
	. take disable file mmap item from default boot menu
	. ask for feedback in motd
	. fix ext2fs on arm (the memory alloced with STATICINIT is flaky on arm)

Change-Id: I7525207074d62abc47ed3891139f6ef7ef6025be
remove libcompat_minix as library

	. get rid of includes in libcompat_minix:
	  . move configfile.h to minix/include/
	  . all others are unneeded as they point to other files
	. merge the .c files with libc

Change-Id: I5e840c66fb9bc484f377926aa9d66473bbd16259