GraphResult function

  DECLARATION:  GraphResult

      PURPOSE:  Returns error code for last graphics operation

         UNIT:  Graph

  RESULT TYPE:  Integer

      REMARKS:  Internal errors in the Graph unit are reported through
                GraphResult.  The value returned reflects the status if the
                last graphics operation.  The following error return codes
                are predefined in the Graph unit:

  ERROR      GRAPHICS ERROR                   CORRESPONDING ERROR
  CODE         CONSTANT                          MESSAGE STRING
 ----------------------------------------------------------------------------
    0       grOK                   No Error
   -1       grNoInitGraph          BGI graphics not installed (use InitGraph)
   -2       grNotDetected          Graphics hardware not detected
   -3       grFileNotFound         Device driver not found
   -4       grInvalidDriver        Invalid device driver file
   -5       grNoLoadMem            Not enough memory to load driver
   -6       grNoScanMem            Out of memory in scan fill
   -7       grNoFloodMem           Out of memory in flood fill
   -8       grFontNotFound         Font file not found
   -9       grNoFontMem            Not enough memory to load font
  -10       grInvalidMode          Invalid graphic mode for selected driver
  -11       grError                Graphics error
  -12       grIOerror              Graphics I/O error
  -13       grInvalidFont          Invalid Font File
  -14       grInvalidFontNum       Invalid Font Number
  -15       grInvalidDeviceNum     Invalid Device Number
 ----------------------------------------------------------------------------

                NOTE:  GraphResult is reset to 0 after it is called.