Bug #1890 Opencv 2.4.0 with QT 4.7.4 and cvcreatebutton exception fixed.

QVector range check exception fixed.
refactored filters in the ocl module; added an accuracy tests for ocl::medianFilter
ocl: perf: use RELATIVE_ERROR in SANITY_CHECK for exp/log/pow
fix imshow under Windows with OpenGL support:

we doesn't create OpenGL windows by default
OpenGL window must be created by user via namedWindow
cmake: cleanup OpenCVModules_TARGETS from cache

This will allow to disable modules between cmake runs
Updated ffmpeg_vesion.cmake after #1516.
Merge pull request #1626 from ilya-lavrenov:ocl_filters
Merge pull request #1640 from alalek:ocl_fix_exp_test
added Khronos OpenCL 1.2 header files
ocl: force to use Khronos OpenCL headers
ocl: update autogenerated code
Merge pull request #1642 from alalek:cmake_cleanup_targets
Merge pull request #1641 from jet47:imshow-opengl-fix
Merge pull request #1459 from asmorkalov:ocv_qt_segflt_fix
Merge pull request #1587 from alalek:opencl_khronos_headers