logilab-common #51957 remove FDCapture from testlib.py and check tests for py3k [validation pending]

remove deprecated FDCapture from testlib.py; then check unittest_testlib for python3. For now, Pytest crashes on unittest_testlib because of it, so we are not sure if it is py3k compatible; of course, since we used it intensively in our test suites for testing the py3k versions of lgc, astng and pylint, it is expected to be all fine

appeared in<not specified>
done in0.54.0
load left0.000
closed by<not specified>