Fix various typos, man page issues and improve the documentation (#415)

This commit makes various different improvements to the documentation:
- sh.1: Backported (with changes) mandoc warning fixes from ksh2020
  for the ksh93(1) man page: <https://github.com/att/ast/pull/1406>
- Removed unnecessary spaces at the end of lines to fix a few other
  mandoc warnings.
- Fixed various typos and capitalization errors in the documentation.
- ANNOUNCE: Document the addition of the ${.sh.pid} variable
  (re: 9de65210).
- libast/man/str*: Update the man pages for the libast str* functions
  to improve how accurately each function is described.
- ksh93/README: Update regression test/compatibility notes to include
  OpenBSD 7.0, FreeBSD 13.0 and WSL running Ubuntu 20.04.
- Change a few places to store the return value from strlen in a
  size_t variable rather than signed int.
- comp/setlocale.c: To avoid confusion of two separate variables named
  lang, the function local variable has been renamed to langidx.

src/cmd/ksh93/tests/arrays.sh

@@ -598,7 +598,7 @@ x=$(
 	foo[1]=(66)
 	typeset -p foo
 ) 2> /dev/null
-[[ $x == "$exp" ]] || err_exit 'setting element 1 to index fooay failed'
+[[ $x == "$exp" ]] || err_exit 'setting element 1 of indexed array foo failed'
 unset foo
 exp='typeset -a foo=((11 22) (x=3))'
 x=$(

src/cmd/ksh93/tests/basic.sh

@@ -536,7 +536,7 @@ if builtin cat 2> /dev/null; then
 	done
 fi
 
-$SHELL -c 'kill -0 123456789123456789123456789' 2> /dev/null && err_exit 'kill not catching process id overflows'
+$SHELL -c 'kill -0 123456789123456789123456789' 2> /dev/null && err_exit 'kill not catching process ID overflows'
 
 [[ $($SHELL -c '{ cd..; print ok;}' 2> /dev/null) == ok ]] || err_exit 'command name ending in .. causes shell to abort'
 

src/cmd/ksh93/tests/coprocess.sh

@@ -29,7 +29,7 @@ fi
 
 bintrue=$(whence -p true)
 
-function ping # id
+function ping # ID
 {
 	integer x=0
 	while ((x++ < 5))

src/cmd/ksh93/tests/functions.sh

@@ -1042,7 +1042,7 @@ function foo
 	typeset pid
 	$tmp1 > $tmp2 & pid=$!
 	wait $!
-	[[ $(< $tmp2) == $pid ]] || err_exit 'wrong pid for & job in function'
+	[[ $(< $tmp2) == $pid ]] || err_exit 'wrong PID for & job in function'
 }
 foo
 # make sure compiled functions work

src/cmd/ksh93/tests/grep.sh

@@ -50,7 +50,7 @@ function grep
 	done
 	noprint=$vflag$cflag$lflag		# don't print if these flags are set
 	integer n=0 c=0 tc=0 nargs=$#		# initialize counters
-	for i in "$@"				# go thru the files
+	for i in "$@"				# go through the files
 	do	if	((nargs<=1))
 		then	fname=''
 		else	fname="$i":

src/cmd/ksh93/tests/sigchld.sh

@@ -126,7 +126,7 @@ then	err_exit "CHLD trap failed -- expected 4 args, got $#"
 elif	(( $4 != 0 ))
 then	err_exit "CHLD trap failed -- exit code $4"
 elif	(( $1 != $2 ))
-then	err_exit "child pid mismatch -- got '$1' != '$2'"
+then	err_exit "child PID mismatch -- got '$1' != '$2'"
 elif	(( $3 != 9 ))
 then	err_exit "child status mismatch -- expected '9', got '$3'"
 fi

src/cmd/ksh93/tests/tilde.sh

@@ -27,7 +27,7 @@ then	x=$(print -r -- ~root)
 	[[ $x == ~root ]] || err_exit '~user expanded in subshell prevent ~user from working'
 fi
 
-function home # id
+function home # ID
 {
 	typeset IFS=: pwd=/etc/passwd
 	set -o noglob