s3: incorrect cache hit

[shykes]

In some situations, s3.Put will hit the task cache, causing the put task to NOT be executed. This is a silent error: the change will appear to be applied successfully, but in reality no upload has taken place.

To reproduce:

1. s3.Put with inputs A. This task will execute correctly.
2. s3.Put with inputs B different from B. For example, file contents may be different. This task wil also execute corectly.
3. s3.Put with inputs A. All inputs must be identical to the first run. THIS TASK WILL BE INCORRECTLY CACHED.

This error is not specific to S3. Any package with side-effects may be affected.

[samalba]

Fixed