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

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