Log Message:
Update to 1.19

Upstream changes:
1.19  Fri Nov 22 07:15 2013
  - Remove the OP tree munging optimization since it wasn't in the
    end really speeding things up. (chocolateboy)
  - Require Time::HiRes explicitly because CentOS cripples the base
    perl install.

1.18  Mon Jun 17 18:07 2013
  - Revert fixes for implicitly-lvalue getters for now since that
    actually breaks user code. It seems it's not just because the
    users are naughty, so more investigation required.

1.17  Mon Jun 17 07:09 2013
  - For Hashes: Implement predicates that check definedness and
    existance explicitly. The traditional "predicates" check
    definedness. It's conceivable to also want a bool-check
    type predicate. File a ticket if you need that.
  - Fix bug regarding getters being implicitly lvalue by
    returning the internal SV*. Instead, we now use TARG.