Update multimedia/pitivi to 0.99
- Patch the runtime dependency checking code in check.py to:
- match the version of GObject Introspection python bindings available in ports (devel/pygobject3-common), and
- load numpy early to ensure the libgcc_s.so.1 library loaded is from ports (lang/gcc7) and not from base.
- Add new port multimedia/gstreamer1-transcoder (separated from pitivi code base)
Note that pitivi version 0.999 has been released, but depends on
gstreamer 1.14 which is not yet in ports.