Refactoring, rename array_enabled to enabled.
Fixed bug when counting number of nodes.

Solves some WebGL conformance tests.
We do not need to fake a NULL, just check the assigned value.
Rename array_buffer_binding with using_vbo.
Fix error when assigning enable.
When a attrib is enabled the buffer could not be bound.
Add an enable function to the varray to handle the enable/disable.
We stop changing the vertex attrib information in the enable.

In the enable function we just enable and recalculate the limits
if required by the attrib. These lines could be needed because
of the previous bugs.
We do not need the enabled in the set function anymore.