removed for easy_install).

Unittests should now call unittest_tools.verify_grad instead of
tensor.basic.verify_grad. The unittest version is simply a wrapper function
which takes care of first seeding the random number gen.

Updated the documentation accordingly

added check for NaN and Inf, fixed bug in DebugMode _Linker so that functions can be reused after raising an error

fixed bug in canonize related to output type-matching.  added fill_chain function. fixed local_mul_specialize too