DOC: minor io.rst edits
TST: json tests to int64 to avoid dtype issues
TST: skip tests if xlrd has lower than needed version
TST: skip pickle tests on not-little endianess
TST: skip test_encoding on non-little endian in test_pytables
TST: skip some stata tests on non-little endian
TST: convered skips on knownfailures to knownfailures (test_pickle/test_stata)
Merge pull request #3898 from jreback/test_fixes

TST: test fixes for various builds (debian)