Confusing naming of fringe i C-code

[Kim F. Storm]

I'm preparing to add customization of the fringe bitmaps, so I'm studying
the code related to the fringe.... Very confusing!

So far, I've come across several different names for the fringes:

`fringe' is primarily used on user visible symbols,

`bitmap' is used without explicit reference to the fringe, e.g. bitmap_type, 
x_draw_bitmap, ...   
This isn't wrong, but it would be clearer to use fringe_bitmap_type,
x_draw_fringe_bitmap, etc.

`bitmap area' is used in several comments, as well as in BITMAP_AREA_FACE_ID (= 
fringe face)

`flags area' seems to be the favourite term throughout the code, e.g.
FRAME_FLAGS_AREA_WIDTH, FRAME_X_RIGHT_FLAGS_AREA_WIDTH, flags_areas_extra, ...

And then there are the mixed forms FRAME_FLAGS_BITMAP_WIDTH and 
FRAME_FLAGS_BITMAP_HEIGHT.

Now that 21.1 is out, this would probably be a good time to clean this up.

-- 
Kim F. Storm <address@hidden> http://www.cua.dk