Check whether a database handle object is valid or not
Support function that verifies that an object holding a reference to a foreign object is still valid for communicating with the RDBMS
dbObjects are R/S-Plus remote references to foreign objects.
This introduces differences to the object's semantics such as
persistence (e.g., connections may be closed unexpectedly),
thus this function provides a minimal verification to ensure
that the foreign object being referenced can be contacted.
a logical scalar.