Adds a lowest-common-denominator function, KPLDeaggregate, for
handling records that might be KPL aggregated. Also adds a function,
DeaggregateAndSplitIfNecessary, to wrap the existing functionality of
SplitMessageIfNecessary with KPL deaggreation.
These functions are handy for non-KCL consumers, like Lambda
functions. KCL automatically applies deaggreation for you.
This change is backwards compatible - the previously exposed function
SplitMessageIfNecessary still does the same things.
