[keep] Allow clients to set a header to disable md5sum calculations in keepstore
The md5sum calculation in Keepstore is expensive. In most cases, the client does it too, so it doesn't make sense for Keepstore to calculate the md5sum for the data being read from its backend. Allow the client to set a header to disable it on demand.
Should this also apply to PUTs ?
What should the default setting be? Should it be configurable with a config parameter?