Removed S3/SimpleDB.py and s3db - this never worked.

Amazon's preferred NoSQL is now DynamoDB anyway.
Revert "push md5_xattr to Config only if xattr module was imported"

This reverts commit f685a131ab0e3575c63e7a8178f7e61d8a247b73.
Revert "fix conditional import xattr module"

This reverts commit 8f9b035ad29cd47e302e4833645ebdc6d66aef4f.
Revert "add --xattr option referring to file system extended attribute containing md5sums"

This reverts commit 730dbcc53ca4bc3d6186a2c9ef5256c52e56a4a2.
Merge branch 'revert-xattr'

Sorry this is not correct.

What will happen if we create the md5_xattr on Monday and
change the file on Tuesday? Unfortunately the old md5_xattr
will still be there and s3cmd will think the file hasn't
changed.  This is not acceptable - we need a way to
disregard md5_xattr if the file has changed, that is if its
size or mtime or ctime has changed. These values will have
to be stored in the xattr and checked by s3cmd before using
the md5 from there.