Make redirections like {varname}>file work with brace expansion off

This is some nonsense: redirections that store a file descriptor
greater than 9 in a variable, like {var}<&2 and the like, stopped
working if brace expansion was turned off. '{var}' is not a brace
expansion as it doesn't contain ',' or '..'; something like 'echo
{var}' is always output unexpanded. And redirections and brace
expansion are two completely unrelated things. It wasn't documented
that these redirections require the -B/braceexpand option, either.

src/cmd/ksh93/sh/lex.c: sh_lex():
- Remove incorrect check for braceexpand option before processing
  redirections of this form.

src/cmd/ksh93/COMPATIBILITY:
- Insert a brief item mentioning this.

src/cmd/ksh93/sh.1:
- Correction: these redirections do not yield a file descriptor >
  10, but > 9, a.k.a. >= 10.
- Add a brief example showing how these redirections can be used.

src/cmd/ksh93/tests/io.sh:
- Add a quick regression test.

src/cmd/ksh93/tests/io.sh

@@ -696,6 +696,10 @@ got=$(export tmp; "$SHELL" -ec \
 [[ $(< $tmp/ast36_b.test.log) == "$exp2" ]] || err_exit 'stdout not correctly redirected to file with EXIT/ERR trap defined (2)' \
 	"(expected $(printf %q "$exp2"), wrote $(printf %q "$(< $tmp/ast36_b.test.log)"))"
 
+# ======
+# Redirections of the form {varname}>file stopped working if brace expansion was turned off
+redirect {v}>$tmp/v.out; echo ok >&$v
+[[ $(<$tmp/v.out) == ok ]] || err_exit '{varname}>file not working with brace expansion turned off'
 
 # ======
 exit $((Errors<125?Errors:125))