Avoid removing imgbuf and decoding the whole image again for reloads.

Using the same testing files as the previous patch,
the results are:

.---------------------------------------------.
|imgbufs     | No patch | Patch #1 | Patch #2 |
|----------------------------------------------
|1imgA.html  |   2/1    |   1/1    |    1/0   |
|2imgSA.html |   3/2    |   1/2    |    1/0   |
|3imgSA.html |   4/3    |   1/3    |    1/0   |
|----------------------------------------------
|2imgA.html  |   4/2    |   2/2    |    2/0   |
|3imgA.html  |   6/3    |   3/3    |    3/0   |
'---------------------------------------------'

n1/n2 means:
  n1 imgbufs were created for first load (empty cache)
  n2 imgbufs were created for reload (cached image)

Notes:
 * Rendering is much faster. Easy to notice with Back operation.
 * Between four to five times on www.welt.de.
 * Corner cases can be more than ten times. Usually, it *feels* faster.

1 files changed, 4 insertions, 0 deletions

diff --git a/dw/widget.cc b/dw/widget.cc
index 82677cc8..e6c2aa76 100644
--- a/dw/widget.cc
+++ b/dw/widget.cc
@@ -164,6 +164,10 @@ void Widget::queueDrawArea (int x, int y, int width, int height)
                  x, y, width, height);
    DBG_OBJ_MSG_START ();
 
+   _MSG("Widget::queueDrawArea alloc(%d %d %d %d) wid(%d %d %d %d)\n",
+       allocation.x, allocation.y,
+       allocation.width, allocation.ascent + allocation.descent,
+       x, y, width, height);
    if (layout)
       layout->queueDraw (x + allocation.x, y + allocation.y, width, height);