Hotfix/support cjk (issue #184)

string.printable is too narrow for non-english users.
I refer to http://stackoverflow.com/a/93029 to strip control characters.

added some test cases:
test_strip_chn (tests.gnsyncTest.testGnsync) ... ok
test_strip_eng (tests.gnsyncTest.testGnsync) ... ok
test_strip_kor (tests.gnsyncTest.testGnsync) ... ok
test_strip_nochange (tests.gnsyncTest.testGnsync) ... ok