Make a few parse fcns accessible to B::Hooks::Parser

Make a few parse fcns accessible to B::Hooks::Parser

This module had made copies of three functions from toke.c many releases
ago, and they stagnated.  Most outside code has no business calling
them, but the least worst choice I believe is to make them accessible,
but hide that fact.

This commit makes them accessible to modules that have defined PERL_EXT.
It does not document their API's, and marks them as subject to change,
so they aren't even listed as available in the docs.  In other words,
you'd have to really go digging to find out you could use them.

And the API of two of the three had changed since the code was
originally stolen.  So that "subject to change" actually has happened.
We should feel free to change the API as needed, and B::Hooks::Parser
will have to be updated.

Thanks to Tony Cook for advising me on this area unfamiliar to me.