Use aws-log-error for HTTP error response codes.
Use http connection pooling.
delete-multiple should check response XML for <error>
put response does not have an entity
Just formatting.
initiate-multipart-upload should call check-response
Update unit tests.

- Do a test of multipart-put with many parts.

- Re-enable the 100-continue test.

- Delete some commented-out debugging code.

- Move some comments.
Delete some commented-out code.
Disable bigger multipart test.

Makes test iterations take too long, while checking for failure in
tracking down the 404 NoSuchUpload problem. Plan to re-enable the test, later.
Delete misleading comment.

Should have been deleted way back at commit 48e9b3b
Append incrementing suffix to bucket names used in `test-bucket-ops`.

Rationale: There can be intermittent errors -- such as a 404
NoSuchUpload for multipart uploads -- when the same name is used to
create, delete and recreate buckets within a short amount of time. As
best I understand it, this is due to redirects and/or DNS updates, as
described here in the AWS docs:

  http://docs.aws.amazon.com/AmazonS3/latest/dev/UsingRouting.html

Because rapid reuse of a bucket name is not typical of real-world usage
-- just of unit tests -- I feel comfortable making the tests _not_ reuse
the same name, in order to avoid such errors. Especially after spending
many, many hours trying to figure out the source of the intermittent
errors, and looking for any other reasonable way to address this.
Re-enable bigger multipart test disabled in commit 7d21afc