TODO: rebase Determining "class" of formula, issue 1058

Code was written by Fredrik Johansson http://code.google.com/p/sympy/issues/detail?id=1058 and I just contribute this to SymPy

I divided it on 2 parts:
sympy/functions/special/classify.py -- code itself
sympy/functions/special/tests/test_classify.py -- test for that

That code was written in August 2008, so may be SymPy alredy has that functional. If it so, please forgive me.