Fix [ \( str -a str \) ], [ \( str -o str \) ]

Symptoms:

$ test \( string1 -a string2 \)
/usr/local/bin/ksh: test: argument expected
$ test \( string1 -o string2 \)
/usr/local/bin/ksh: test: argument expected

The parentheses should be irrelevant and this should be a test for
the non-emptiness of string1 and/or string2.

src/cmd/ksh93/bltins/test.c:

- b_test(): There is a block where the case of 'test' with five or
  less arguments, the first and last one being parentheses, is
  special-cased. The parentheses are removed as a workaround: argv
  is increased to skip the opening parenthesis and argc is
  decreased by 2. However, there is no corresponding increase of
  tdata.av which is a copy of this function's argv. This renders
  the workaround ineffective. The fix is to add that increase.

- e3(): Do not handle '!' as a negator if not followed by an
  argument. This allows a right-hand expression that is equal to
  '!' (i.e. a test for the non-emptiness of the string '!').

src/cmd/ksh93/tests/bracket.sh

@@ -447,7 +447,19 @@ fi
 [ abc =~ 'a(b)c' ] 2>/dev/null || err_exit "[ abc =~ 'a(b)c' ] fails"
 [ abc =~ '\babc\b' ] 2>/dev/null || err_exit "[ abc =~ '\\babc\\b' ] fails"
 [ AATAAT =~ '(AAT){2}' ] 2>/dev/null || err_exit "[ AATAAT =~ '(AAT){2}' ] does not match"
-[ AATAATCCCAATAAT =~ '(AAT){2}CCC(AAT){2}' ] || err_exit "[ AATAATCCCAATAAT =~ '(AAT){2}CCC(AAT){2}' ] does not match"
+[ AATAATCCCAATAAT =~ '(AAT){2}CCC(AAT){2}' ] 2>/dev/null || err_exit "[ AATAATCCCAATAAT =~ '(AAT){2}CCC(AAT){2}' ] does not match"
+
+# string nonemptiness tests combined with -a/-o and parentheses
+for c in "0:x -a x" "1:x -a ''" "1:'' -a x" "1:'' -a ''" \
+	 "0:x -o x" "0:x -o ''" "0:'' -o x" "1:'' -o ''" \
+	 "0:x -a !" "0:x -o !" "1:'' -a !" "0:'' -o !"
+do	e=${c%%:*}
+	c=${c#*:}
+	eval "[ \( $c \) ]" 2>/dev/null
+	(($?==e)) || err_exit "[ \( $c \) ] not working"
+	eval "test \( $c \)" 2>/dev/null
+	(($?==e)) || err_exit "test \( $c \) not working"
+done
 
 # ======
 exit $((Errors<125?Errors:125))