Recently test_exceptions was reporting random
memory leaks. It seems that this was caused
by the pickling part of testAttributes, which
uses a random integer for pickling protocol.
With this patch applied, I couldn't reproduce
the leak anymore, although I didn't run it 666
times.
The patch also includes a fix for the pickling
part of the test (previously it was checking
the attributes of the original exception, not
the unpickled one), removes another unused
import and moves all the imports to the
top of the file.