tty/pty: change back default CERASE to ^H

Alternatives should be considered (such as changing our keymaps to
better match NetBSD) in due time, but for now, the current default
is incredibly annoying!

Change-Id: I4cab5d6a9f39983ee8aa80362768fdb9cf3db948
tty/pty: unbreak stty(1)

Change-Id: I3f857dcbb89e18c7db3a72f4bd6809beb7904bc0
VFS: complete the devmajor_t/devminor_t switch

Change-Id: I9f809283f19d577cf7e02705fdbb2310ae2b6cba
PTY: let closed master cause EOF on slave

This puts PTY on par with e.g. rs232 as well as behavior documented
for other OSes.  It is not a fix for an issue in userland, though.

- add a (minimal) test case to test77;
- fix a few other minor issues in test77.

Change-Id: I89c000921ee69dd9f5713665349c1ab1ad1dc2cc