don't evaluate bool(Relational)
Merge remote-tracking branch 'rlamy/Relational' into relational

Conflicts:
	sympy/core/relational.py
Update the docstring of Relational.
Remove extra sorting step from tests whenever possible.
Test chebyshevt_root and chebyshevu_root with valid arguments.
Always specify the sort key when sorting.
Don't rely on the truth value of Rational.
Fix for python 3.
Test for issue 2832.
Edit docstring of GreaterThan.
Merge pull request #2350 from jrioux/relational

Relational: bool(Relational) should raise

Continuation of #1646. See issue 2832.