cdms2 (NetCDF) maximum dimension name length is 256

```python
import cdms2
import MV2

a = MV2.ones((12,12))
ax = cdms2.createAxis(MV2.arange(12))
ax.id = "1234567890"*26
print len(ax.id)
a.setAxis(0,ax)


with cdms2.open("bad.nc","w") as f:
    f.write(a)
```

seems to be limited by C variable `MAX_NC_NAME` which likely comes from NetCDF