Fix an ask test failure

True and False are S.true and S.false, so use == instead of is to test for
them.
Fix some tests about hermitian and antihermitian assumptions

Based on the known facts in ask.py, hermitian and antihermitian are some kind
of "extension" of real and imaginary, respectively. Since hermitian ->
~antihermitian, if an expression is known to be real, it must be hermitian,
and thus cannot be antihermitian.