Fix issue 3700

- Manualintegrate changes:
    - Rewrite rule: do not use if integrand cannot be evaluated with manualintegrate
    - Substitution rule: do not use ConstantTimesRule if constant == 1
    - Added test
Fix typos in usage of manualintegrate in _eval_integral
integrate: do not use manualintegrate if the result has dummy variables
manualintegrate: don't use substitution if a subsequent integrand can't be evaluated
Merge pull request #2136 from lidavidm/issue_3700

Fix issue 3700