RasterIO resampling: operate on the full width of a raster whose block width is the raster width, prefer doing chunks in height

git-svn-id: https://svn.osgeo.org/gdal/trunk@28126 f0d54148-0727-0410-94bb-9a71ac55c965
Add optimized versions of resamplers for UInt16

git-svn-id: https://svn.osgeo.org/gdal/trunk@28127 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_travis_macosx