It creates and returns a PSPP::Reader object which can be used to read
data and dictionary information from C<filename>.
+=head3 get_case_cnt ()
+
+Returns the number of cases in a open system file. Some files
+do not store the number of cases. In these instances undef
+will be returned. Therefore, then programmer must check that the
+returned value is not undef before using it.
+
=cut
sub get_dict