FUNCTION dir2name, filename

; Description: This function takes a file name with a full directory path and
;              returns the file name without the directory path.
;
; Input Parameters:
;
;   filename - STRING - The full directory path and file name to be processed.
;
; Return Value:
;
;   The input parameter "filename" is returned with the directory path removed.
;   For example, for the filename '/data/dmb/ngc7789.fits', the function would 
;   return the string 'ngc7789.fits'. 
;     In more detail, if the parameter "filename" is not a string, then the 
;   function returns an empty string ''. If the parameter "filename" does not 
;   contain any instances of the character '/', then the function returns the 
;   parameter "filename". If the parameter "filename" contains instances of 
;   the character '/', then the function returns the last string of characters 
;   after the last instance of the character '/', even if this is the empty
;   string ''.
;
; Author: Dan Bramich (dmb@ing.iac.es)
;
; History:
;
;   19/05/2008 - Module created (dmb)

;Check that "filename" is a scalar string

;If "filename" is an empty string, then return an empty string

;Decompose "filename" into individual characters

;Find the occurrences of "/" in "filename"

;If "filename" does not contain any instances of the character "/", then
;return "filename"

;If "filename" does contain instances of the character "/", then return 
;the last string of characters after the last instance of "/", even if 
;this is the empty string