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).

NEWS

@@ -11,6 +11,10 @@ Any uppercase BUG_* names are modernish shell bug IDs.
   based on the incorrect assumption the IFS would never be larger
   than a single byte.
 
+- Fixed a bug that caused the sleep builtin to continue after being given
+  an unrecognized option. 'sleep -: 1' will now show a usage message and
+  exit instead of sleep for one second.
+
 2020-07-23:
 
 - Fixed an infinite loop that could occur when ksh is the system's /bin/sh.