Fix another test/[ corner case bug; add --posix test script

This fixes another corner case bug in the horror show that is the
test/[ comand.

Reproducer:

   $ ksh --posix -c 'test X -a -n'
   ksh: test: argument expected

Every other shell returns 0 (success) as, POSIXly, this is a test
for the strings 'X' and '-n' both being non-empty, combined with
the binary -a (logical and) operator. Instead, '-n' was taken as a
unary primary operator with a missing argument, which is incorrect.

POSIX reference:
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html
> 3 arguments:
> * If $2 is a binary primary, perform the binary test of $1 and $3.

src/cmd/ksh93/bltins/test.c:
- e3(): If the final argument begins with a dash, always treat it
  as a test for a non-empty string, therefore return true. Do not
  limit this to "new flags" only.

src/cmd/ksh93/tests/posix.sh:
- Added. These are tests for every aspect of the POSIX mode.

src/cmd/ksh93/include/version.h

@@ -21,7 +21,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.0.0-beta.2"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2022-03-05"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2022-03-10"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2022 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */