Fix how unrecognized options are handled in 'sleep' and 'suspend' (#93)

When a builtin is given an unrecognized option, the usage information
for that builtin should be shown as 'Usage: builtin-name options'. The
sleep and suspend builtins were an exception to this. 'suspend' would
not show usage information and sleep wouldn't exit on error:

$ suspend -e
/usr/bin/ksh: suspend: -e: unknown option
$ time sleep -e 1
sleep: -e: unknown option

real	0m1.00s
user	0m0.00s
sys	0m0.00s

src/cmd/ksh93/bltins/sleep.c:
- Show usage information and exit when sleep is given an unknown
  option. This bugfix was backported from ksh2020: https://github.com/att/ast/pull/1024

src/cmd/ksh93/bltins/trap.c:
- Use the normal method of parsing options with optget to fix the
  suspend builtin's test failure.

src/cmd/ksh93/tests/builtins.sh:
- Add the ksh2020 regression test for getting the usage information
  of each builtin. Enable all /opt/ast/bin builtins in a subshell
  since those should be tested as well (aside from getconf and uname
  because those builtins fallback to the real commands on error).

src/cmd/ksh93/bltins/sleep.c

@@ -62,6 +62,8 @@ int	b_sleep(register int argc,char *argv[],Shbltin_t *context)
 			errormsg(SH_DICT,ERROR_usage(2), "%s", opt_info.arg);
 			break;
 	}
+	if(error_info.errors)
+		errormsg(SH_DICT, ERROR_usage(2), "%s", optusage(NULL));
 	argv += opt_info.index;
 	if(cp = *argv)
 	{