Fix issue 3700

Changes:

- Manualintegrate:
    - Rewrite rule: do not use if integrand cannot be evaluated with manualintegrate
    - Substitution rule: do not use ConstantTimesRule if constant == 1
    - Added test
    
Fixes [issue 3700](https://code.google.com/p/sympy/issues/detail?id=3700), but note that the integrand still needs to be `expand`ed to be evaluated.