backlighting again

[AVKuznetsov]

Hi,

My first letter led to some discussion on other subject,
but the question is still opened.

There is commented code in macro.c and help.etx which is disabled
for NEdit 5.4. The code implements the variable $backlight_string
and the function set_backlight_string() allowing to operate by
backlighting via macro.

$backlight_string
  The current value of the window's backlighting specification.
  This is empty if backlighting is turned off. It can be changed
  through calls to the built-in macro function set_backlight_string().

set_backlight_string( [string] )
  Applies the given string, which should be in the format of the
  nedit*backlightCharTypes X resource, to the current text window,
  turning on   backlighting.  If the value of the string passed is
  "default", or if no parameter is passed, the nedit.backlightCharTypes
  X resource's own value will be used.  If the empty string, "",
  is passed, backlighting will be turned off.

The uncommented code is well compiled and stable works.
Let us uncomment it and give to users an facility to change
backlighting via macro.

Alexey Kuznetsov