ExtendedS3Storage: incorrect implementation of exists

[sachin-j-joshi]

Problem description
Currently the ExtendedS3Storage implements exists() by calling listObjects with given path and checking whether list returned is empty or not.
For the path that corresponds with full path to the object this is correct. However this breaks when the path checked is a prefix. In this case list of other object matching that prefix will be returned and the code will incorrectly determine that object exists.

Problem location
ExtendedS3Storage . doExists

Suggestions for an improvement
Instead of listObjects use getObjectMetadata.