Change errors from const strings to vars, DropIfExists to accept n+1 tbls
Change errors from const strings to vars (#82) * #81: Change errors from const strings to vars * #81: Change DropIfExists to accept n+1 tbls, Refactor check errors in tests
Change errors from const strings to vars (#82) * #81: Change errors from const strings to vars * #81: Change DropIfExists to accept n+1 tbls, Refactor check errors in tests