[perl #24847] [patch] simplify register stacks (remove code duplication)

[Matt Fowles]

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All~

This patch sets up a generic register stack (using macro's for values
that change) that the real register stacks can then implement. This was
discussed on list several months ago, but nobody ever got around to it.
So I did ;-)

I am not entirely certain how to fix the manifest, but I did try...
Other than that all tests pass for make test and make testj. make testP
still has one failing test (timer 3) but that failed before.

Hopefully this will reduce code duplication a little :-)

Matt