Make parallel video writer test pass if compiled without threading support
remove a warning on Linux
fix a error in doc
Merge pull request #438 from bitwangyaoyao:2.4_fixwarings
Merge pull request #434 from taka-no-me:fix_parallel_writer_test
added 8u type support to filterSpeckles function
Use gtest assertions in cascade test

This simplifies test debugging a lot
Merge pull request #441 from jet47:filter-speckles-8u
Merge pull request #443 from taka-no-me:fix_cascade_test