Pass WARNS=3

Homogenize usage messages: make the 'usage' word all lowercase, as this seems
to be the most common practice in our tree.

Move UCB-licensed code from 4-clause to 3-clause licence.

Patches provided by Joel Baker in PR 22249, verified by myself.

%d is 12 chars, not 10 chars. hinted by deraadt

Support command -p, -v and -V as posix
Stop temporary PATH assigments messing up hash table
Fix sh -c -e "echo $0 $*" -a x (as posix)
(agreed by christos)

Fixes from David Laight:
- ansification
- format of output of jobs command (etc)
- job identiers %+, %- etc
- $? and $(...)
- correct quoting of output of set, export -p and readonly -p
- differentia

Fixes from David Laight:
- ansification
- format of output of jobs command (etc)
- job identiers %+, %- etc
- $? and $(...)
- correct quoting of output of set, export -p and readonly -p
- differentiation between nornal and 'posix special' builtins
- correct behaviour (posix) for errors on builtins and special builtins
- builtin printf and kill
- set -o debug (if compiled with DEBUG)
- cd src obj (as ksh - too useful to do without)
- unset -e name, remove non-readonly variable from export list.
(so I could unset -e PS1 before running the test shell...)

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Fix command name in error message for 'sh nonexistingfile'.

remove redundant declarations and nexted externs.

compile with WARNS = 2

Be more retentive about use of NOTREACHED and noreturn.

Delint.

PR/5315: Dan Winship: options parsing code should print errors to stderr.

Fix compiler warnings.

NO_HISTORY->SMALL

Fix PR/3258 sh -c 'echo $0' causes segmentation fault.

kill 'register'

Getopts bugs again (I'll never get this right).
- make sure that OPTIND is set correctly even in the absence of options.
- don't keep stale state between getopts calls.

Fix bug in getopts code where the argument list got truncated.
From Todd Miller.

Fix miscellaneous getopts problems:
- the 3 argument version of getopts would not reset properly
- OPTARG did not get cleared after a non argument option was found
- OPTIND was not set properly after

Fix miscellaneous getopts problems:
- the 3 argument version of getopts would not reset properly
- OPTARG did not get cleared after a non argument option was found
- OPTIND was not set properly after a non argument option.

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Fix problems that gcc -Wall found (from Todd Miller, OpenBSD)

PR/2808: POSIX 1003.2: first arg after -c cmd is $0, remainder $1...
(from FreeBSD)

- Add getoptsreset to be used as a callback function when OPTIND is set.
This is used to implement the POSIX behavior when OPTIND=1
- Call setvarsafe instead of setvar. If one ran
"getopts optstr

- Add getoptsreset to be used as a callback function when OPTIND is set.
This is used to implement the POSIX behavior when OPTIND=1
- Call setvarsafe instead of setvar. If one ran
"getopts optstr badvariable"
where badvariable contained an illegal variable name, there was no way
to recover, since setvar() would longjmp on the error.

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getopts fixes:

1. OPTIND value was not computed correctly when the argument was part of the
option string (i.e. for "l:" "-l 1" was working "-l1" was not). (PR/2505).
2. OPTARG was not being unse

getopts fixes:

1. OPTIND value was not computed correctly when the argument was part of the
option string (i.e. for "l:" "-l 1" was working "-l1" was not). (PR/2505).
2. OPTARG was not being unset in case of errors [in the non POSIX error case].
3. optvar could be set to random values.
4. Option string starting with a : was not treated specially as POSIX
specifies (if the option string starts with a :, then there is no
error printed when there are missing option arguments or illegal options,
and OPTARG and optvar are being set specially).
5. Implemented getopts "opts" optvar [arg]. The optional argument case
was not implemented.

To do:
- what does Posix say about resetting the getopts state? Bash does it
by setting OPTIND=0; is that correct? Should we be doing the same thing?
- should we be using getopt(3) for everything internal to the shell? Is that
feasible because we might need to handle multiple invocations at once.

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Merge in my changes from vangogh, and fix the x=`false`; echo $? == 0
bug.

Reverted to set - turning off -x and -v. Charles corrected me... It is part
of POSIX.