Deprecate Parrot_compreg

[whiteknight]

The Parrot_compreg function registers a C function pointer as an NCI PMC in the IGLOBALS_COMPREG_HASH global. This is only used by IMCC, and is not really a sustainable solution. Basic NCI PMCs do not follow the interface suggested in PDD31, although that's not really the biggest problem here.

A much more sustainable solution would be a function which takes a compiler PMC and registers it. IMCC and any other utility that wants to, can create it's own NCI PMC and register that through the same interface.

I would like to deprecate the Parrot_compreg function and replace it with a more sustainable and extendable interface.

[coke]

The code in Parrot_compreg is similar to that in the <compreg> opcode;
please take care not to break the op as part of this ticket.

[whiteknight]

I have added the deprecation notice for this function, It will go away shortly after 3.6. I will take special care to not harm the compreg op, and will increase test coverage of that op if necessary.

[whiteknight]

As promised, Parrot_compreg was removed from master. This was all dead code, and there was no change in behavior with the compreg opcode.