bugfix: memory leak

[niu2x]

i think CommandBufferGL::setVertexBuffer and CommandBufferGL::setIndexBuffer should do same things.

1. check weather new value is different from old value.
2. release old value, retain new value.

there's memory leak in CommandBufferGL::setVertexBuffer if not release old value

[niu2x]

checks fail due to: /usr/bin/ld: cannot find -lXxf86vm. it's not my fault...