Package namespace and Safe init cleanup for plperl [PATCH]

This is the final plperl patch in the series from me.

Changes in this patch:

- Moved internal functions out of main:: namespace
    into PostgreSQL::InServer and PostgreSQL::InServer::safe

- Restructured Safe compartment setup code
    to generalize and separate the data from the logic.

Neither change has any user visible effects.

This patch will apply cleanly over the 'Add on_trusted_init and
on_untrusted_init to plperl' patch:
https://commitfest.postgresql.org/action/patch_view?id=271

Tim.