Log message:
make it clear what package depend on

discussed with wiz@.

Log message:
Import transformers-compat-0.3.3 as devel/hs-transformers-compat,
packaged for wip.

This package includes backported versions of types that were added to
transformers in transformers 0.3 an 0.4 for users who need strict
transformers 0.2 or 0.3 compatibility to run on old versions of the
platform, but also need those types.

Those users should be able to just depend on transformers >= 0.2 and
transformers-compat >= 0.3.

Note: missing methods are not supplied, but this at least permits the types
to be used.