Disallow >;word and <>;word for 'redirect' (re: 7b59fb80, 7b82c338)

The >;word and <>;word redirection operators cannot be used with
the 'exec' builtin, but the 'redirect' builtin (which used to be
an alias of 'command exec') permitted them. However, they do not
have the documented effect of the added ';'. So this commit blocks
those operators for 'redirect' as they are blocked for 'exec'.

It also tweaks redirect's error message if a non-redirection
argument is encountered.

src/cmd/ksh93/sh/parse.c: simple():
- Set the lexp->inexec flag for SYSREDIR (redirect) as well as
  SYSEXEC (exec). This flag is checked for in sh_lex() (lex.c) to
  throw a syntax error if one of these two operators is used.

src/cmd/ksh93/sh.1, src/cmd/ksh93/data/builtins.c:
- Documentation tweaks.

src/cmd/ksh93/sh/xec.c, src/cmd/ksh93/bltins/misc.c:
- When 'redirect' gives an 'incorrect syntax' (e_badsyntax) error
  message, include the first word that was found not to be a valid
  redirection. This is simply the first argument, as redirections
  are removed from the arguments list.

src/cmd/ksh93/tests/io.sh:
- Update test to reflect new error message format.

src/cmd/ksh93/tests/io.sh

@@ -528,7 +528,7 @@ actual=$(redirect 2>&- 3>&2; echo ok)
 [[ $actual == ok ]] || err_exit "redirection error in 'redirect' causes exit"
 
 # Test that 'redirect' does not accept non-redir args
-expect=$'*: redirect: incorrect syntax\n status = 2'
+expect=$'*: redirect: incorrect syntax: /dev/null/foo\n status = 2'
 actual=$( (redirect /dev/null/foo) 2>&1; echo " status = $?" );
 [[ $actual == $expect ]] || err_exit 'redirect command accepts non-redirection argument' \
 	"(expected $(printf %q "$expect"), got $(printf %q "$actual"))"