Test for `forward.grad` on functions using `ifelse` fails.

[Non-Contradiction]

The problem is caused by issues in handling ifelse and rep for JuliaObject in JuliaCall.
The corresponding test is temporarily commented out.

[Non-Contradiction]

Note the test has been added back and is okayl because of some tricks in JuliaCall as documented in the progress.md.
Need to think on the issue further, so leave it open as a reminder.

[nashjc]

Difficulties with any "switch" within a program are likely. Good to keep as a reminder.