Rename travis_test.sh to test_travis.sh

It was breaking ./bin/t<TAB> -> ./bin/test and it was driving me nuts.
Make test_travis.sh not executable
Add tests for issue #3626
Try to predict a correct number of taylor terms for function expansions with non-atomic argument, e.g. sin(sqrt(x)).series(x)
log(Product(...)) -> Sum(log(...))
Revert "Make test_travis.sh not executable"

This reverts commit 85886937514ae3d3f5105f45542d6d717ae03ee8.

Travis doesn't work if it isn't executable.
log(Product) -> Sum(log) requires simplify
log(Product(arg)) simplifies if arg.f.is_positive
Remove dummy=True option for Symbol() and numbered_symbols()
Use Symbol(...) instead of Symbol(..., dummy=True) in risch.py for debugging
An error in solve for Piecewise.