Deparse the /d flag with implicit features

Deparse the /d flag with implicit features

Before the recent feature revamp (2fc860ee1e0), loading the
unicode_strings feature would always set the feature_unicode %^H ele-
ment, even though the core did not actually use it.  Now it is some-
times not set.  So we have to check the hint bits as well.  Since
feature.pm has it hardcoded, load feature.pm to get the right bit.

The stuff with $feature_bundle_mask is redundant, but it avoids load-
ing feature.pm unnecessarily.