eval_pmc branch ready for testing

[Andrew Whitworth]

The eval_pmc branch is passing all tests for me, and is ready for some
more eyes. The branch removes the Eval PMC. It is replaced in most
cases by PackfileView, which has a different interface and more
features. As an example of a change:

$P0 = compreg 'PIR'
$P1 = $P0(code)
$P1()

Would be replaced by this sequence:

$P0 = compreg 'PIR'
$P1 = $P0(code)
$P2 = $P1.'main_sub'()
$P2()

PackfileView doesn't implement the invoke vtable like Eval did, and
has a few other interface differences. All parrot tests pass for me,
but I know that there is a problem with nqp-rx where INIT blocks are
either not being invoked or are not being invoked reliably. I'm still
tracking this down. Winxed appears to run fine. I am going to try new
NQP and Rakudo later, after I get nqp-rx sorted out.

More eyes would be appreciated. I would like to get this branch
mergable and merged in the next week or two, so I can move on to other
projects.

Thanks,

--Andrew Whitworth