Fix fullscreen clients with gravity != NorthWest (#1764)

Once upon a time, 4b9584fdb1 already fixed this problem: We have to
set the border width to zero before applying the new geometry to the
client, because changing the border width makes the client move
according to its gravity.

Then came e54387904b and made this code use awful.placement instead
of just fullscreening the client itself (without explaining why in the
commit message!). After this commit, the border width was just ignored
and left as-is. This was then fixed in 0bf8bb6a64 (no idea which
callback the commit message refers to, the old code was basically just
c.border_width=0, c:geometry(screen_geo)). However, now the border width
was again changed after the geometry and the bug that was fixed by
4b9584fdb1 was back.

This commit fixes this regression again by making sure that the border
width is set to zero before the geometry is set. This becomes slightly
more complicated, because now it is also awful.placement's job to
restore the old border width.

This is why this commit adds a new option to awful.placement so that it
sets the border width to zero after creating its memento of the old
border width.

Fixes: https://github.com/awesomeWM/awesome/issues/1607
Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/awful/ewmh.lua

@@ -292,18 +292,14 @@ function ewmh.geometry(c, context, hints)
 
         if original_context == "fullscreen" and beautiful.fullscreen_hide_border ~= false then
             props.ignore_border_width = true
+            props.zap_border_width = true
         end
 
-        aplace[context](c, props)
-
-        -- Remove the border to get a "real" fullscreen.
-        if original_context == "fullscreen" and beautiful.fullscreen_hide_border ~= false then
         local original = repair_geometry_lock
         repair_geometry_lock = true
-            c.border_width = 0
+        aplace[context](c, props)
         repair_geometry_lock = original
     end
-    end
 end
 
 client.connect_signal("request::activate", ewmh.activate)

lib/awful/placement.lua

@@ -352,6 +352,9 @@ end
 -- @treturn The drawin's area.
 area_common = function(d, new_geo, ignore_border_width, args)
     -- The C side expect no arguments, nil isn't valid
+    if new_geo and args.zap_border_width then
+        d.border_width = 0
+    end
     local geometry = new_geo and d:geometry(new_geo) or d:geometry()
     local border = ignore_border_width and 0 or d.border_width or 0