Change grid dim
Use shared memory

copy clusters positions into shared memory to speed up checking distance
Squashed commit cleanup:

commit 16f70b2e7a464d2d6bfc07886a8613aec3ce6032
Author: Tomek Janiszewski <janiszt@gmail.com>
Date:   Tue Jun 11 22:59:44 2013 +0200

    Chagne distance to return distance^2

commit 5efc4a8ec1b400fecf3ec23eeecc855148a7ccec
Author: Tomek Janiszewski <janiszt@gmail.com>
Date:   Tue Jun 11 22:55:22 2013 +0200

    Remove unused functions

commit 4f1ddf9b1ead94de60bc8a2164481ca283f17cc9
Author: Tomek Janiszewski <janiszt@gmail.com>
Date:   Tue Jun 11 22:43:35 2013 +0200

    Stop passing global variable as a parameter

commit 6c8077a94f118b230c35482388fa209cad4d4bd2
Author: Tomek Janiszewski <janiszt@gmail.com>
Date:   Tue Jun 11 22:36:58 2013 +0200

    Use constns defines instead of variable in find... kernel

commit 58cb3830057ea54816b2e030731a56ad3416e017
Author: Tomek Janiszewski <janiszt@gmail.com>
Date:   Tue Jun 11 22:35:16 2013 +0200

    Move global variable up