Synopsis:

       retval=db_ixopen(db_handle,field_nr/name,ntxfilename)

Arguments:

       db_handle - database handle returned from db_open()

       field_nr/name - The field number or name of the field

       ntxfilename - Full path to the NTX filename

Description:  This function opens an NTX clipper index file associated with the DBF file specified by the db_handle.     The field_nr/name specifies either the field number (numbered from 0) or the actual name of the field in the DBF for which the index file references.

Typically each DBF file will have one or more index files each associated with one of the fields in the DBF file.   Currently only Clipper NTX index files are supported.

Returns:   Returns 0 upon success or a negative error code.