Zero division error

This pull request has two part.
First, 0 * Float('inf') was 0 while Float('inf') * 0 was nan.
Now they are both nan.
Second, 1/S(0) was oo while 1/Float(0) was a ZeroDivisionError.
Now 1/Float(0) gives Float('inf').

This allow
Or(Eq(x,0), 1/x  >1 ).subs(x,0)

See also
http://code.google.com/p/sympy/issues/detail?id=3595
and 
https://github.com/sympy/sympy/pull/1868