add poOtherHeaders

For use with eg, the Internet Archive S3 interface.

Also example program which created https://archive.org/details/joeyh-test

Closes https://github.com/aristidb/aws/issues/119
switch to poAutoMakeBucket

Maxwell worried that allowing arbitrary nonstandard headers could cause
silent data loss if they were sent to a S3 endpoint that did not support
them. This avoids that problem, by only supporting the IA's
x-amz-auto-make-bucket header. If a server ignores that header, no data is
lost, although of course trying to PutObject into a bucket that does not
exist will fail.
updated example to use poAutoMakeBucket
Merge pull request #120 from joeyh/master

add poOtherHeaders