kshareddatacache: Adopt KSDCCorrupted for exceptional errors.

This involves converting many present assertions (which crash no matter
what) and error-code return values (which have to be checked everywhere
the return value is used at) into using the KSDCCorrupted exception.

The nice thing about using the exception is that it can be trapped and
handled so that it does not cause an application crash.

There's still a bit more to do -- the end goal is that all accesses to
shm, no matter how minor, are vetted beforehand to ensure it won't cause
a page fault or bus violation.

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