Python3 bindings for opencv matching system opencv version.

Please note that python3-numpy is a runtime dependency as
well as a build time dependency. Installing the resulting
python3-opencv package without python3-numpy already installed
will create unpredictable behaviour i.e.
  first install python3-numpy
  then  install python3-opencv

By default, additional "contrib" modules are included. If these
are not wanted, set the CONTRIB environment variable to 0
e.g.
  CONTRIB=0 bash python3-opencv.SlackBuild

A successful installation can be quickly tested by runnng the
ocv-test.py script found in the documentation directory

OPTIONAL EXTRAS
  The following installations are automatically detected and
used if available at build time:
 - VTK visualization and image processing
 - libdc1394 IIDC/DCAM/Firewire based camera control
 - zulu-openjdk17 Java Development Kit
   (other Java varieties probably also work)
 - apache-ant Java build tool
  (only relevant if Java is also detected)
