specify an error handling scheme for character conversion. Additional
scheme "utf-8" in read mode. Unicode input filenames are now
supported by design. The values of the pax_headers dictionary are now
limited to unicode objects.

Fixed: The prefix field is no longer used in PAX_FORMAT (in
conformance with POSIX).
Fixed: In read mode use a possible pax header size field.
Fixed: Strip trailing slashes from pax header name values.
Fixed: Give values in user-specified pax_headers precedence when
writing.

Added unicode tests. Added pax/regtype4 member to testtar.tar all
possible number fields in a pax header.

Added two chapters to the documentation about the different formats
tarfile.py supports and how unicode issues are handled.