term-mode, ESC AnSiT, and screen

term-mode, ESC AnSiT, and screen

[Mark Plaksin]

If term-mode sees ESC AnSiTc DIR, it updates default-directory based on
the DIR provided.  term-mode also uses AnSiTu (u for user) and AnsiTh
(host).  With these you can track the directory even if you are on a
remote host.  Send the right host, user, and directory, and you can use
TRAMP to load files from the remote host.  It's wonderful!

It fails to work if you run screen inside your term-mode buffer.  screen
discards ESC A so you just end up with 'nSiTc DIR' displayed on the
screen.  Thinking this was a screen bug, I asked the screen folks about
it.  So far they have asked if ANSI X3.64 says you should preserve or
discard undefined escape sequences.  And, of course, they asked if
term-mode could use a different sequence :)

Was ESC A selected because it wasn't defined and it should be passed
through?  Everything besides screen passes it so I'm guessing that
everything but screen is doing the right thing :)

Thanks!