PRO safe_fits_read, file, ext, maxtry, data, header, status

; Description: This module tests that a FITS image file is available on disk
;              before reading in the image data corresponding to the specified
;              image extension. If the file is not available, then the
;              module waits 1 second before trying again. The module will
;              attempt to read in the image data a total of "maxtry" times
;              before giving up and returning a status of zero.
;
; Input Parameters:
;
;   file - STRING - The full directory path and file name of the FITS image file
;                   to be read in.
;   ext - INTEGER/LONG - The FITS file image extension for which the image data is
;                        to be read in. If "ext" is set to a negative number, then
;                        the image extension is not given explicitly to the module
;                        "fits_read", which means that "fits_read" will consequently
;                        determine the image extension in which the image data 
;                        resides.
;   maxtry - INTEGER/LONG - Maximum number of attempts at reading the image data
;                           before giving up and returning the "status" value of 
;                           "0" (Default value = 1).
;
; Output parameters:
;
;   data - SAME AS FITS FILE - The image data that has been read in from the FITS file.
;   header - STRING VECTOR - The corresponding image header read in from the FITS file.
;                            The module removes the keywords BZERO and BSCALE, since
;                            the image is read in without any offset or scaling applied.
;   status - INTEGER - If the module successfully read in the image data, then "status"
;                      is returned with a value of 1, otherwise it is returned with
;                      a value of 0. 
;
; Author: Dan Bramich (dan.bramich@hotmail.co.uk)
;
; History:
;
;   19/04/2008 - Module created (dmb)

;Check that "file" is a variable of STRING type

;If "ext" is not a number of the correct type, then let the module "fits_read" determine
;the image extension to be read in

;If "maxtry" is not a positive number of the correct type, then reset its value to "1"

;Wait until the input file is available

    ;If "ext" is non-negative, then feed the specified extension number to the module
    ;"fits_read"

    ;If "ext" is negative, then let "fits_read" determine which image extension contains
    ;the image data

;Remove the BZERO and BSCALE keywords from the header