Plane class
Removed trailing spaces
Merge https://github.com/sympy/sympy into plane
Changed the are_perpendicular and is_parallel method
Refactor code in projection_line method
XFAIL the test in test_args
Removed the XFAIL
Added Dummies and used free_symbols() instead of is_constant()
compare frozensets as Basic objects

It was wrongly being assumed that if a frozenset was encountered that
it was equal to the other frozen set. This caused arbitrary sorting
of args like Min(1,x) and Min(2,x) since they are both the same function
with a single frozenset argument...but the (1,x) should be less than the
(2,x). So rather than returning 0, the args of the frozenset(s) are
compared.
changed Dummy() to Dummy
Add tests to test_wester.py for set theory and continued fractions.

Also for symbolic continued fractions.
Removed Trailing Space error
Merge pull request #7682 from clsn/cftests

Add tests to test_wester.py for set theory and continued fractions.
Merge pull request #7667 from akshayah3/plane

Plane class
Redirect standard error to void
Redirect both stdout and stderr to void
Merge pull request #7731 from debugger22/redirect-std-error

Redirect standard error output to void
Merge pull request #7727 from smichr/compare

compare frozensets as Basic objects (re-addresses #958)
add unchanged function to pytest
move NS to pytest