Split/Join tests

Transpose dot opt

pep8 + missing imports

Windows doc fix

Besides fixing some typos, I removed the part about the installation
problems, which sounded a bit scary (after all we provide installation
instructions that are supposed to work).

The old form (PatternSub) had the problem that it wasn't calling broadcast_like
on the return value.  It would have been wrong to hack a broadcast_like into
gof.opt, so I rewrote these two optimizations as a function.

PatternSub is a really cool idea, in the future it might be worth writing a
TensorPatternSub that deals with tensor-specific issues, like casting,
dimshuffles, and rebroadcasts.

Review/tests for ExtractDiag and trace

added a hint to the BadOptimization exception

Fix div by zero in tensor grad

Correctly do version comparison: fix #136

misc cleanup and a bugfix in linalg ops

added sparse dot