test_support.requires(): Instead of raising TestSkipped, raise a new

test_support.requires():  Instead of raising TestSkipped, raise a new
exception, ResourceDenied.  This is used to distinguish between tests that
are skipped for other reasons (platform support, missing data, etc.) from
those that are skipped because a "resource" has not been enabled.  This
prevents those tests from being reported as unexpected skips for the
platform; those should only be considered unexpected skips if the resource
were enabled.