can't delete file attribute

[chaosphere2112]

import cdms2
f=cdms2.open("attribute.nc","w")
f.my_Att = "Anything"
del(f.my_Att)'

gives us

Segmentation fault (core dumped)

Migrated from: CDAT/cdat#1398

[doutriaux1]

might be already fixed

[doutriaux1]

we should just add a test if not in already

[dnadeau4]

https://github.com/UV-CDAT/cdms/blob/master/tests/test_regressions.py#L41