switch OS X base SDK to 10.7
Several VoxelSystems can have different view frustum
Merge pull request #874 from Atlante45/master

Several VoxelSystems can have different view frustum
Merge pull request #872 from ey6es/ssao

Performance improvement for the SSAO blur step, cleanup.
Merge pull request #873 from birarda/master

switch OS X base SDK to 10.7