Update from version 0.17 to version 0.19.

Pkgsrc changes:
- Adjust dependencies

Upstream changes:
0.19    Sun Aug 23 15:03:02 EDT 2009
        - un-fix coercions on parameterized types, since it broke
          MooseX::Method::Signatures, as well as any other code that relied on
          new type constraint objects being generated each time a type was
          parameterized (hdp).

0.18    Sat Aug 22 12:50:42 EDT 2009
        - fix coercions on parameterized types (Hans Dieter Pearcey).

(seb)