Fix various cases with 3 or 4 parameters in test(1) to be POSIX compliant.
More precisely, this gives precedence to an interpretation not using the
'(', ')', '-a' and '-o' in their special meaning, if possible. For example,
it is now safe to write [ "$a" = "$b" ] and assume it compares the two
strings.

The man page already says that test(1) works this way, so does not need to
be changed.

Interpretation of input with more parameters tries a bit harder to find a
valid parse in some cases.

Add various additional test cases to TEST.sh.

PR: standards/133369
Approved by: ed (mentor)