Update benchmark script.

The 'delegate_2' and 'delegate_3' benchmarks were raising exceptions on
their first call.

Now prints a 'speed-up' factor comparing to getting/setting an
attribute of a new style class.
Fix embarassing error.
Machines are too fast, we need more resolution!
One last issue with time reports.
Some more improvements to benchmark script.
Merge pull request #54 from enthought/traits-benchmark

Update benchmark script.