#4223 namespace test failures

[Don Porter]

Tests namespace-old-9.5 and
namespace-28.1 fail on the HEAD
because they test the complete
result of [namespace import] evaluated
in the global namespace.

The TIP 329 temp implementation
imports new commands [try] and
[throw] into ::, changing the
result. Since this may well not
be a permanent feature, adding
them to the expected list is the
wrong fix.

A better fix is to run at least
the [namespace import] tests, if
not the entire namespace*.test
collections of tests, in some
child namespace over which the
testing collection can claim
complete control.

error.test is an example of
one such scheme.

[Donal K. Fellows]

Fixed using a temporary namespace to provide more control. Excellent suggestion.