3d_scalar seg faults on mac

The following script seg faults on my mac. It works on linux. Upgrading to opengl2 might fix this. @doutriaux1 @aashish24 Do we test 3D plots?

```python
import vcs
import cdms2
f=cdms2.open("http://test.opendap.org/dap/data/nc/coads_climatology.nc")
x=vcs.init()
s=f["AIRT"]
gm=x.get3d_scalar()
x.plot(s,gm)
```

