AttributeDict does not support hasattr()

[orbeckst]

AttributeDict does not support hasattr() but it should:

import gromacs

ad = gromacs.utilities.AttributeDict(a=1, b=2)

assert hasattr(ad, "a")
assert not hasattr(ad, "x")    # raises AttributeError from KeyError

Using in is a workaround:

assert "a" in ad
assert "x" not in ad

[jandom]

Here is my little proposal of a fix #269