TODO for AT&T ksh93, 93u+m bugfix branch

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Fix regression test failures:

- On OpenBSD, there are 15 locale-related test failures in variables.sh.
- There are many regression test failures on NetBSD.

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Fix build system:

- ksh does not currently build on AIX or QNX.
- On NetBSD 9.0, the build fails if /bin/sh is used as $SHELL (the default)
  as iffe writes line numbers directly into generated header files. The cause
  needs to be investigated. It could be a regression in NetBSD 9.0 sh.
  Workaround: bin/package make SHELL=/some/other/shell
- Reimport the removed nmake. It is necessary for changes in Makefiles
  to take effect. The machine-generated Mamfiles are now used as a fallback,
  but they are not meant to be edited by hand.

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Fix currently known bugs affecting shell scripting. These are identified by
their modernish IDs. For exact details, see code/comments in:
https://github.com/modernish/modernish/tree/0.16/lib/modernish/cap/

- BUG_BRACQUOT: shell quoting within bracket patterns has no effect. This
  bug means the '-' retains it special meaning of 'character range', and an
  initial ! (and, on some shells, ^) retains the meaning of negation, even
  in quoted strings within bracket patterns, including quoted variables.

- BUG_CMDEXPAN: if the 'command' command results from an expansion, it acts
  like 'command -v', showing the path of the command instead of executing it.
  For example:
	v=command; "$v" ls
  or
	set -- command ls; "$@"
  don't work.
  See also: https://github.com/att/ast/issues/963

- BUG_CMDSPEXIT: preceding a "special builtin"[*] (other than 'eval', 'exec',
  'return' or 'exit') with 'command' does not always stop it from exiting
  the shell if the builtin encounters error.
  [*] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_14

- BUG_CSUBSTDO: If standard output (file descriptor 1) is closed before
  entering a $(command substitution), and any other file descriptors are
  redirected within the command substitution, commands such as 'echo' will
  not work within the command substitution, acting as if standard output is
  still closed.

- BUG_IFSGLOBS: In glob pattern matching (as in case or parameter
  substitution with # and %), if IFS starts with ? or * and the "$*"
  parameter expansion inserts any IFS separator characters, those characters
  are erroneously interpreted as wildcards when quoted "$*" is used as the
  glob pattern.

- BUG_LOOPRET2: If a 'return' command is given without a status argument
  within the set of conditional commands in a 'while' or 'until' loop (i.e.,
  between 'while'/'until' and 'do'), the exit status passed down from the
  previous command is ignored and the function returns with status 0
  instead.