NAME:
  repchar
 PURPOSE:
  Replace a target string with a new string in string or string array.
 DESCRIPTION:
 CATEGORY:
  Utility
 CALLING SEQUENCE:
  result = repchar(str,c1,c2)
 INPUTS:
  str - input string or string array to be scanned
  c1  - Target string, if found will be replaced with c2
 OPTIONAL INPUT PARAMETERS:
  c2  - Replacement string for target, default = ' '
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  return value is the modified string, input not modified
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
    96/07/02 - Written by Marc W. Buie, Lowell Observatory