Use Piecewise in manualintegrate (issue 3647)
manualintegrate checks assumptions on symbols
Don't cache integral results in case assumptions change
manualintegrate: check symbol assumptions in u-substitution as well
manualintegrate: add piecewise arctangent integrals
manualintegrate: use Q.zero instead of Q.is_true
manualintegrate: don't duplicate alternative rules
Merge pull request #2504 from lidavidm/issue_3647

Issue 3647