Cursor images are fairly small and having one pool for each image adds
a lot of unnecessary overhead. Instead, create one large pool and
allocated all cursor images from that.
In order to do that, however, the code that creates shm surface needed
some refactoring. This patch adds a new struct shm_pool that is used
by the cursor and also changes struct window to use it.
Ander Conselvan de Oliveira
001de54ea1