tabs are 8 space wide

Kup and Kdown move the cursor up and down

various desktop-y keybindings

soft-tabs

thanks to mkhl and neutralinsomniac (and probably other guys at
9front)

INSTALL: build arm64 binaries on arm64 Macs

If there is any x86 binary in the chain of parent processes from
the current one, then uname -m prints x86_64 and clang
defaults to building x86_64 binaries.

Detect arm64 using the kernel version and force building
an arm64 toolchain instead of perpetuating x86.

This is particularly important when the user shell is rc,
which has been built for x86, because then rebuilding
under rc continues to use x86.

src/cmd/acme: provide info on presense or absence of undo history (#528)

It's sometimes useful to know whether there's been editing activity
in a window. This PR adds that information to the ctl file.

Change-Id: I21a342ac636dd5c7701b3ed560e3526867329c2c

cmd/auxstats: improve network device name matcher in Linux

cmd/auxstats: improve wireless interface name matcher in Linux

mk: provide a mechanism to default to `rc`

For cross-compiling plan9 from Unix, provide a way
to force `mk` to use `rc` instead of `sh` without
setting `MKSHELL` in individual `mkfile`s.

If the environment variable `FORCERCFORMK` is set,
`mk` will default to using `rc`, not `sh`.

Signed-off-by: Dan Cross <cross@gajendra.net>

sam: fix spurious overwrite message

Fixes:

% sam -d
-.
w foo
foo: (new file) #0
w foo
?warning: write might change good version of `foo'

acme: fix extra print args

lib9p: Fix compile error

commit 385a6d5877258cee0cac6151e6359c9206006b01 removed src/lib9p/_post.c
from the code base, but overlooked removing a reference to the
_post.o object file from the src/lib9p/mkfile.

This results in lib9p failing to compile:

* Running on Darwin...
* Compiler version:
Apple clang version 12.0.5 (clang-1205.0.22.11)
* Building mk...
* Building everything (be patient)...
>>> mk: don't know how to make '/Users/sasha/plan9port_fork/lib/lib9p.a(_post.o)' in /Users/sasha/plan9port_fork/src/lib9p
mk: for i in ... : exit status=exit(1)

Remove _post.o from the list of dependent object files from
src/lib9p/mkfile to have lib9p compile.

Fixes: 385a6d587725 ("lib9p: Remove postmountsrv (#505)")

lib9p: Remove postmountsrv (#505)

.gitignore: Ignore some more things that get created during compile.

9term: Skip unnecessary ioctl call on AIX.