when passing a fileobj into tarfile.open() without
specifying the type open() will try openers in their
dict key order from TarFile.OPEN_METH.  This can fail
if the order changes.

This patch adds a tell() and seek() on failure of
openers.  fileobjs must already support these methods
to work so this makes no new requirements.

OpenOrderTest uses a dict-alike with shuffled keys to
try and provoke the wrong orders for openers.

Let me know if it looks good and I'll check it in.

Made the testcase simpler and checked it in as rev. 53161 and rev. 53162 (2.5).