NAME: 
  ldcalir
 PURPOSE: 
  Load calibration information for OSIRIS XD data from a calib file.
 DESCRIPTION:
 CATEGORY:
  Spectroscopy
 CALLING SEQUENCE:
  ldcalir,calibfile,calib,valid
 INPUTS:
  calibfile - Name of calibration file to read.
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  CALIBPATH - Path to location to look for calibration files (flat).
                 The default is the current directory.
  SILENT    - Flag, if true suppresses all informational output.
  NOFLAT    - Flag, if true suppresses loading the flat field image.
 OUTPUTS:
  calib - anonymous structure with calibration information
           tag contents and usage:
              height - height of slit in pixels.
              nor    - number of orders in spectral image.
              por    - maximum polynomial order for wavlength calibration.
                         quadratic=2
              slope  - slope of each order (dy/dx).
              x1     - starting x value of each order.
              x2     - ending x value of each order.
              y0     - y value at bottom of slit for x=0 for each order.
              flat   - Strip format flat image.
              flatname- Name of flat field image loaded.
              cof    - Wavelength calibration poly coeffs [nor,por].
              npts   - Total number of points (all orders)
              w      - Wavelength values for each order [npts].
              o      - Range of points in each order [nor,2].
  valid - Flag, if true indicates a valid calibration set was loaded.  The
            contents of calib are unreliable if this flag is false.
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  95/09/14, Written by Marc W. Buie, Lowell Observatory
  96/05/27, MWB, changed structure organization and added a new, improved
                 file format.
  97/12/18, MWB, added NOFLAT keyword