sympy/sympy — pull request #8568 by avichaldayal (2014-12-05 13:21:58+00:00)
Title: Substitution in order should take care of NegativeInfinity

Fixes #7872

The following substiution now works:
```
In [1]: O(x**3).subs(x, exp(-x**2))
Out[1]:
⎛ 2 ⎞
⎜ -3⋅x ⎟
O⎝ℯ ; x → -∞⎠
```