Remember to copy the additional headers in the memory cache

Reported by Coverity (about an uninitialized boolean).
MemoryCache: remove support for saving and loading of the data

This was a relict from 2009 which has not been used for ages.
Abandon LightMessageDataBundle

The whole point of this class was to prevent the tiny overhead of one uint.
Given that this class is only used in an uncommon case where user doesn't want
the perisstent caching and in the unit tests, it isn't worth the extra code
(which contained an obvious bug which was only uncovered by the coverity scan,
but was obscure enough to not be hit that often in the wild).
Add missing breaks

Thanks to Coverity for catching this.
Fix a copy-paste error courtesy of Coverity