Fix python2->3 pickle bug for exprs with floats
Fix python2->3 pickle bug for exprs with floats

Dumping a pickled sympy expression containing a float in Python 2,
then loading it in Python 3 generates an error. This is due to
sympy's compatibility shim for `long` on Python 3 using `int`, which
doesn't support the "L" suffix when converting from a string. This
commit removes that suffix if present.

kaushik94/sympy,kaushik94/sympy,kaushik94/sympy