Mayvi plot3d gets glitchy with many significant digits

Reporting against 3.3.0-1 on Ubuntu, which is the latest deb I could find.

```
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=10.04
DISTRIB_CODENAME=lucid
DISTRIB_DESCRIPTION="Ubuntu 10.04.4 LTS"
```

Compare the visualization of these two plot3d calls:

```
mlab.plot3d([ 600000.63287674, 600000.63697936, 600000.66607347,
600000.67137776], [ 600000.4572601 , 600000.56022494, 600000.68954629,
600000.82019476], [1, 1, 1, 1], [1, 1, 1, 1])
```

vs.

```
mlab.plot3d([ 0.63287674, 0.63697936, 0.66607347,
0.67137776], [ 0.4572601 , 0.56022494, 0.68954629,
0.82019476], [1, 1, 1, 1], [1, 1, 1, 1])
```

The first call produces something very broken visually -- jerky motion, wrong shapes, missing parts of the tubes.

The second call works as expected.