Validate batch checks, vector integretity in unit tests

Drill provides a BatchValidator that checks vectors. It is disabled by default. This enhancement adds more checks, including checks for row counts (of which there are surprisingly many.)

Since most operators will fail if the check is enabled, this enhancement also adds a table to keep track of which operators pass the checks (and for which checks should be enabled) and those that still need work. This allows the checks to exist in the code, and to be enabled incrementally as we fix the various problems.