ArrayWithAttrs doesn't copy attrs dictionary

[rwb27]

When copying/creating new ArrayWithAttrs objects, the attrs dictionary is sometimes shared between the copies (e.g. if you slice an ArrayWithAttrs). This can cause very odd behaviour if you're not expecting it.

[rwb27]

I've amended the code so that in aray_finalize it always copies the attributes dictionary.

[rwb27]

Interestingly, copying the attrs dictionary doesn't always solve the problem; if you've got numpy ndarrays in there, they don't get copied (as the dict only stores a reference to them). I've explicitly copied all the ndarray objects (and subclasses) to get around this.