Updated bundle adjustment in stitching module: 1) it minimizes reprojection error now, 2) it minimizes error over focal, aspect, p.p.x, p.p.y parameters. Refactored and updated warpers.

added convert functions to BruteForceMatcher_GPU
other minor fixes

added stream support to downsample, upsample, pyrUp and pyrDown

added gpu::buildWarpPlaneMaps and gpu::buildWarpCylindricalMaps functions, integrated into stitching

GPU: updated upsample, downsample functions, added pyrDown, pyrUp, added support of 16S filtering; put spherical warper on GPU (from opencv_stitching)

fixed BFM warning ("cannot tell what pointer points to")

HAVE_CONFIG_H -> HAVE_CVCONFIG_H

minor optimization of SURF_GPU (reduce memory transfers, use structure of arrays instead of array of structures)

added downsample function into gpu module, refactored it a little bit, added guard for CUDA related include in cascadeclassifier_nvidia_api.cpp

[~] Refactored, cleaned up, and consolidated the code of GPU examples (cascadeclassifier and cascadeclassifier_nvidia_api)