Regress tests: keep common code in one place

src/cmd/ksh93/tests/_common:
- Added. This keeps one common version of 'err_exit', 'warning',
  and other init code.

src/cmd/ksh93/tests/*.sh:
- Source _common as a dot script.
- Remove 50-odd, occasionally slightly different, versions of the
  common code.
- Some minor tweaks.

src/cmd/ksh93/tests/shtests

@@ -345,9 +345,6 @@ do	[[ $i == *.sh ]] || i+='.sh'
 		glob.sh)	grep -c '^[[:blank:]]*test_[a-z]\{3,\}' $i ;;
 		*)		grep -c err_exit $i ;;
 		esac	)
-	if	(( t > 2 ))
-	then	(( t = t - 2 ))
-	fi
 	tests[$i]=$t
 	T=test
 	if	(( t != 1 ))