aws s3 cp doesn't work with prefix

From a bucket containing millions of files, I want do download a few thousand based on their prefix.

Note: using --exclude "*" --include "myprefix" works, but is impractical since it lists all the files and applies the filter afterwards.

The problem is aws s3 cp adds a trailing "/" after the prefix I specify. In the example below you can see that logs/2015-08-17 becomes logs/2015-08-17/
This additional "/" leads to an empty result set, since the keys in the bucket have the form logs/YYYY-MM-DD-HH-MM-SS-RANDOM).

> aws s3 cp s3://mybucket/logs/2015-08-17 . --recursive --dryrun --debug

2015-08-17 21:48:32,026 - MainThread - awscli.clidriver - DEBUG - CLI version: aws-cli/1.7.27 Python/2.7.6 Linux/3.14.13-c9, botocore version: 0.108.0
2015-08-17 21:48:32,026 - MainThread - awscli.clidriver - DEBUG - Arguments entered to CLI: ['s3', 'cp', 's3://mybucket/logs/2015-08-17', '.', '--recursive', '--dryrun', '--debug']
....
2015-08-17 21:48:32,088 - MainThread - botocore.endpoint - DEBUG - Making request for (verify_ssl=True) with params: {'query_string': {u'prefix': u'logs/2015-08-17/', u'encoding-type': 'url'}, 'headers': {}, 'url_path': u'/mybucket', 'body': '', 'method': u'GET'}

Start by reproducing the documented `aws s3 cp` recursive dry run with `--debug` and inspect how the S3 prefix is formed. Done means a prefix such as `logs/2015-08-17` is queried without an added trailing slash and matching keys are returned.

Written by the indexing model from the issue text.