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

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Fix regression test failures:

- On FreeBSD, there is a test failure in [[ -N file ]] in bracket.sh.
- On OpenBSD, there are 15 locale-related test failures in variables.sh.

______
Fix build failures:

- ksh does not currently build on NetBSD, AIX, HP-UX, Solaris, or QNX.

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Fix or remove broken or misguided default aliases:

- Make a proper POSIX 'hash' builtin command and remove the builtin alias
  hash='alias -t --', which, when removed, exposes a b0rken 'hash' builtin.
  To work with this alias, the 'alias' builtin parses the '-r' for 'hash'
  *after* '--' ('alias -t -- -r'), which is utterly bogus and violates POSIX.

- Make a proper builtin out of the redirect='command exec' alias. It should
  really only parse redirections. Currently, if an unwitting user notices this
  alias and tries out something like 'redirect ls >file', it does 'exec ls
  >file', so 'ls' replaces their shell and they get logged out. That is so
  misdesigned I'm calling it a bug.
     Alternatively, maybe just get rid? Who uses this anyway? 'redirect >&2'
  takes four more keystrokes to type than 'exec >&2'.

- Make proper builtins out of the following scripting-related aliases, so
  that 'unalias -a' does not eliminate them. If done correctly, this causes
  no other change in behaviour. It would be good practice to 'unalias -a' in
  a script to start with a clean slate, except ksh has always made that
  impossible without losing these. Default aliases should be to facilitate
  interactive use.
	- autoload='typeset -fu'
	- compound='typeset -C'
	- float='typeset -lE'
	- functions='typeset -f'
	- integer='typeset -li'
	- nameref='typeset -n'
	- source='command .'
  Keep these default aliases for the benefit of interactive shells:
	+ history='hist -l'
	+ r='hist -s'
	+ stop='kill -s STOP'
	+ suspend='kill -s STOP $$'

______
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_CMDSPASGN: preceding a "special builtin"[*] with 'command' does not
  stop preceding invocation-local variable assignments from becoming global.
  [*] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_14

- 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_KUNSETIFS: ksh93: Can't unset IFS under very specific circumstances.
  unset -v IFS is a known POSIX shell idiom to activate default field
  splitting. With this bug, the unset builtin silently fails to unset IFS
  (i.e. fails to activate field splitting) if we're executing an eval or a
  trap and a number of specific conditions are met.

- 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.

- BUG_MULTIBIFS: We're on a UTF-8 locale and the shell supports UTF-8
  characters in general (i.e. we don't have WRN_MULTIBYTE) – however, using
  multi-byte characters as IFS field delimiters still doesn't work. For
  example, "$*" joins positional parameters on the first byte of IFS instead
  of the first character.