Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

sh: Include <limits.h> instead of non-standard <sys/limits.h>.

sh: Remove the "exp" builtin.

The "exp" builtin is undocumented, non-standard and not very useful.

If exp's return value is not used, something like
VAR=$(exp EXPRESSION)
is equivalent to
VAR=$((EXPRESSION))
except that errors in the expression are fatal and quoting special
characters is not needed in the latter case.

If exp's return value is used, something like
if exp EXPRESSION >/dev/null
can be replaced by
if [ $((EXPRESSION)) -ne 0 ]
with similar differences.

The exp-run showed that "let" is close enough to bash's and ksh's builtin
that removing it would break a few ports. Therefore, "let" remains in 9.x.

PR: bin/104432
Exp-run done by: pav (with some other sh(1) changes)

sh: Apply set -u to variables in arithmetic.

Note that this only applies to variables that are actually used.
Things like (0 && unsetvar) do not cause an error.

Exp-run done by: pav (with some other sh(1) changes)

sh: Fix some warnings in code for arithmetic expressions.

Submitted by: eadler

sh: Detect dividing the smallest integer by -1.

This overflows and on some architectures such as amd64 it generates SIGFPE.
Generate an error on all architectures.

sh: Import arithmetic expression code from dash.

New features:
* proper lazy evaluation of || and &&
* ?: ternary operator
* executable is considerably smaller (8K on i386) because lex and yacc are
no longer used

Differences from dash:
* arith_t instead of intmax_t
* imaxdiv() not used
* unset or null variables default to 0
* let/exp builtin (undocumented, will probably be removed later)

Obtained from: dash