Use x-amz-copy-source header without leading /
Use x-amz-copy-source header without leading /

Fixes #10.

kahing/s3proxy,kahing/s3proxy,andrewgaul/s3proxy,andrewgaul/s3proxy,bouncestorage/s3proxy,bouncestorage/s3proxy,flandr/s3proxy,flandr/s3proxy,timuralp/s3proxy,timuralp/s3proxy