ENH: make siftfast compilation optional

CMake/ImportSiftFast.cmake

CMake/otbConfigure.h.in

CMake/otbIncludeDirectories.cmake

CMakeLists.txt

Code/FeatureExtraction/CMakeLists.txt

Examples/Patented/CMakeLists.txt

...sicFilters/otbPointSetDensityEpanechnikovFunctionTest.cxx

Testing/Code/BasicFilters/otbPointSetDensityFunctionTest.cxx

...e/BasicFilters/otbPointSetDensityGaussianFunctionTest.cxx

Testing/Code/FeatureExtraction/CMakeLists.txt

...ng/Code/FeatureExtraction/otbFeatureExtractionTests10.cxx

Testing/Utilities/CMakeLists.txt

Testing/Utilities/otbUtilitiesTests.cxx

Utilities/CMakeLists.txt