Relational.canonical: put symbol on lhs
FiniteSet.contains: use Eq to check inclusion

If an object defines the _eval_Eq method, it can be used
to test whether an object is not in the set.
Interval: relax test for inclusion; do symbolic reversal test
use prec with _eval_evalf, not evalf (which uses dps)
Set.as_relational: slightly simplify code
Sets: shorten line lengths
Sets: add tests
inequalities: minor edits
edit inequalities error messages
don't rewrite with re and im parts

By rewriting in terms of re and im parts allows the resulting expression
to give False instead of the proper error that should occur if something
with im(x) != 0 is used in a Relational.
reduce_rational_inequalities
discard (-oo, oo) from Intersection

Without this commit, `bin/test contin -k _P` will fail in the
previous commit. After the next commit that changes
solve_univariate_inequality, the test will no longer fail but
the issue still exists: (-oo, oo) is not removed.
solve_univariate_inequality
update tests