added test for bug #1448 and hopefully fixes the bug #2898
increased time limits in perf tests
increased epsilon in sanity test
disable tests that requires video support if it is not available
fixed minMax perf test
exploring possible bug in optimize_linear_svm
Turn on OpenCL by default
Refactor OpenCL search
Allow OpenCL acceleration in every OpenCV module
Move OpenCL SURF to nonfree module
SURF accuracy test is moved to nonfree
Trying to make ocl surf work

1. Added more sync to reduction.
2. Turned off Image2D feature. Probably its support is not detected correctly.
3. Temporary disabled descriptor tests - can't localize a problem of the ocl descriptor.
Refactor OpenCL initialization and allow to use ocl module witout explicit setup
Disable crashing ocl tests
Move OpenCl SURF perf tests to nonfree and fix build of samples
Fixed wrong in row index of SSE implementation in prefilterXSobel function.
Fix build errors
add hack to disable optimization of linear svms; improved precision of optimize_linear_svm; add the relevant test, which however requires some big database (so it's disabled by default)
Merge pull request #675 from jet47/gpu-test-fixes

GPU test fixes
Merge pull request #676 from vpisarev/svd_stuff

added test for bug #1448 and hopefully fixes the bug #2898