BUG: Fix input bytes conversion in Py3 to return str
Fixes #3963, #4785

Fixed bug with reading compressed files in as `bytes` (`gzip` and `bz2` both now return `bytes` rather
than `str` in Python 3) rather than `str` in Python 3, as well as the lack of conversion of `BytesIO`. Now, `_get_handle` and `_wrap_compressed` both wrap in an `io.TextIOWrapper`, so that the parsers work internally only with `str` in Python 3. In Python 3.2, has to read the entire file in first (because `gzip` and `bz2` files both lack a `read1()` method in 3.2)

Also adds support for passing fileobjects with compression == 'bz2'.
