Previously, misinterpreted that os.access(file, X_OK)
always returns True on Solaris. Yes, but only for
the uid of 0. Python issue #13706 closed "not a bug"
reads to "just use os.stat()", so we went to great
lengths to do so quite exhaustively.
But this is wrong -- *only* when root, should we check
the file modes -- os.access of X_OK works perfectly
fine for non-root users.
And, we should only check if any of the executable bits
are set. Alas, it is true, you may execute that which
you may not read -- because as root, you can always read
it anyway.
Verified similar solution in NetBSD test.c (/bin/test),
OpenBSD ksh for its built-in test, and what FreeBSD/Darwin
for their implementation of which.c.