test_cmdline: add special char challenges, implement default mtime for mfile/mdir.
test_cmdline: remove unnecessary call to time.time().
test_cmdline: add test_stdin_one_recent_no_sep.
clitest: don't use sys.stdout.encoding for decoding test process' out/err.
test_cmdline: add stdin unicode challenge test.
test_cmdline: add TestSpecialChars.test_stdin_two_recent.