Fixes #6988

Now, expand_log(exp(x), force=True) == x
Test for fix of issue #6988
8517: fix Line3D intersection

o increase coverage and correct code
o remove dead code (I don't think the call to solve will every return {})
o remove code that handles the cases that the reversal of args handles
o make sure line routines accept tuples as points
make 3D collinear lines parallel as in 2D
Merge pull request #8548 from lezorich/iss6988

Issue #6988: expand_log(exp(x), force=True) = x
Merge pull request #8546 from smichr/geom

8517: fix Line3D intersection
Add _complement helper for EmptySet, rename few sets methods from complement to _complement
Fix solve_poly_inequality for constant polys

Was:
In [5]: solve_poly_inequality(Poly(0, x), '==')
Out[5]: []

In [6]: solve_poly_inequality(Poly(1, x), '==')
Out[6]: []
reduce_rational_inequalities: substitute correct polys for True/False

fixes #8545
Cleanup solve_rational_inequalities
Cleanup: remove extra imports from doctests of inequalities.py
Merge pull request #8550 from skirpichev/8545-fix

reduce_rational_inequalities: substitute correct polys for True/False
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
edit error message