DIO__InitializeDevice (ul_pbar_dio)

 *  Synopsis:
 *    #include <ul_pbar_dio:dio.h>
 *
 *    CDIOptr DIO__InitializeDevice( int *errorCode, const int retryCount,
 *				      const char *deviceName )
 *
 *  Function intent:
 *    DIO__InitializeDevice() requests the DI for the specified ACNET device.
 *    If successful it returns a unique DIO device I/O control pointer for use
 *    in future DIO__xxx() calls.
 *  Function parameters:
 *    int	*errorCode	DIO I/O status/error code - returned
 *    int	retryCount	# of retry attempts to use on DIO__xxx calls
 *    const char *deviceName	pointer to device name string
 *  errorCode return values:
 *    DIO_OK		success
 *    CLIB_MEMFAIL	memory allocation failed
 *    DIO_BADARG	invalid ACNET device name
 *    DIO_MEMFAIL	memory allocation failure in dio routine
 *    negative value	ACNET format error indicating overall failure
 *  Function return value:
 *    NULL		ACNET I/O error or memory alloc error - see errorCode
 *    otherwise		unique DIO device I/O control pointer