NAME:
  axextend
 PURPOSE:   (one line only)
  Adjust an axis plot range
 DESCRIPTION:
  This function replicates the direct graphics option of extending the
    axis plot range so that data do not touch the sides of the plotting
    box or axis tick marks.  This is really only needed for the new plot
    functions added in IDL v8.0
 CATEGORY:
  Plotting
 CALLING SEQUENCE:
  outrange=axextend(inrange)
 INPUTS:
  inrange - two element vector with the input range, presumed to be the
              exact data range for the plot.
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  EXTEND - Fraction to extend the plot range by.  Default=0.05 (5%).
 OUTPUTS:
  Return value is the extended plot range
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2011/01/07, Written by Marc W. Buie, Southwest Research Institute