GenomeDiagram tweak for Python 3 (using py33 ReportLab branch)

The forthcoming ReportLab v3 release will natively support
Python 2.7 and 3.3 onwards. This work is currently available
as the py33 branch on their BitBucket repository, which I
used to test this simple string change (bytes versus unicode).
Python 3 fix for ColorSpiral test: sort dictionary entries
Further relax stochastic test output

(This should reduce the number of false postives on the buildbots)