enabled initMultiArrayBorder() to handle asymmetric borders
introduced VIGRA_SINGLE_THREADED preprocessor flag
made FFTWPlan initialization threaded-safe; refactored FFTWCorrelatePlan and correlateFFT()
replaced detail::setZeroBorders() with initMultiArrayBorder()
cmake: improved configuration of multi-threaded programs
updated files according to the vigra repo
Replaced the std::sort by faster std::nth_element for the median filter. Also did major work on the fast normalized cross-correlation algorithm. It now uses the vigra IntegralImage creation facilities and became much more generic. At least it should work for images/arrays with 1,2 or 3 dimensions. Higher dimensions may be added with a smarter accessor function to the integral images. These are currently hard coded for 1,2 and 3-dimensional arrays. And the best... all test are still running.