Log Message:
Changes 1.7.1:
* Fixed the build process for MacOS X.
* Re-activeted vigra-config (script to query VIGRA installation information)
  and added VigraConfig.cmake (query VIGRA installation information from within
  cmake).
* Added CDash support (nightly builds and tests).
* Added convexHull().
* Added vigra::Box.
* Added vigra::Sampler class to sample given data in various ways.
* Added much new functionality to the vigra::RandomForest class (e.g. more
  split strategies, variable importance measures, feature selection)
* Added readSIF() (reader for the Andor SIF file format).
* Added vigra::HDF5File for easier navigation in HDF5 files.
* Added recursive approximation of the Gaussian filter
  (recursiveGaussianFilterX(), recursiveGaussianFilterY())
* vigranumpy: added Gabor filtering.
* Fixed multi-threading bugs at various places.
* Minor improvements and bug fixes in the code and documentation.