Make satisfiable() work with arbitrary expressions, not just Symbols

This is in the same spirit as https://github.com/sympy/sympy/pull/2451.

This also should make satisfiable() more deterministic by sorting the symbols.
Fix spelling error in function name
Merge branch 'master' into satisfiable_expr

Conflicts:
	sympy/logic/tests/test_inference.py
candidate fix for get_motion_params() bug

- Change integration style.
- Update tests to accomodate integration style change.
- doc revision for get_motion_params()
Merge branch 'master' into satisfiable_expr
Change to gmail address in AUTHORS for Amit Saha
Merge pull request #2506 from asmeurer/satisfiable_expr

Make satisfiable() work with arbitrary expressions, not just Symbols
Merge pull request #2553 from amitsaha/master

Change to gmail address in AUTHORS for Amit Saha
Split gmpy & matplotlib tests again (to 3 splits)
Merge pull request #2545 from zanzibar7/get_motion_params_bugfix

candidate fix to get_motion_params() for issue #2543

close #2543
Merge pull request #2555 from skirpichev/travis-3

Split gmpy & matplotlib tests again (to 3 splits)