Return Limit instance if limit function can't compute the limit

Before: PoleError exception was raised
Calling powerset() method should not produce deprecation warnings

Use is_subset(S.Reals) instead of is_real.
MinMaxBase will raise error if args are not Expr's

This also fix deprecation warnings like this:
>>> s = FiniteSet(FiniteSet(1, 2, 3))
>>> s
{{1, 2, 3}}
>>> len(s)
1
>>> s.powerset()
/usr/lib/python3.3/site-packages/sympy-0.7.5_git-py3.3.egg/sympy/functions/elementary/miscellaneous.py:334:
SymPyDeprecationWarning:

is_real has been deprecated since SymPy 0.7.6. Use is_subset(Reals)
instead. See https://github.com/sympy/sympy/issues/6212 for more info.
Merge pull request #3 from skirpichev/is_real_deprecated

MinMaxBase will raise error if args are not Expr's
Explicitly test physics/quantum/qubit/qubit_values
Changed deprecation for lambdify matrices

This commit changes how lambdify behaves, mostly having to do with the
deprecation plan to change the default from Matrix -> numpy.matrix to
Matrix -> numpy.array.

- No longer have the `default_array` kwarg. Everything is solved by
  passing in a custom dict for the `modules` kwarg.

- Throw warning only if expr is a matrix, and the translation for
  `Matrix` hasn't been set at all by the user. If it has, no warning
  is thrown, as the translation is intentional.
Merge pull request #8269 from amitsaha/is_real_deprecated

Calling powerset() method should not produce deprecation warnings
Merge pull request #8034 from jcrist/issue_8030

Change behavior of lambdify deprecation
Refactor tests in test_qubit
Update test_qubit.py

Remove unneeded whitespace
Add test for issue 7245

fixes #7245
Add test for issue 7602

fixes #7602
Don't use _eval_sides to evaluate Equality, use is_zero instead

fixes #6116
Move _eval_sides to the Relational._eval_simplify helper
Slightly expand Equality docstring: add notes about simplification
Merge pull request #8284 from skirpichev/7245-7602-tests

Add tests for issues 7245 and 7602
Merge pull request #8270 from skirpichev/6116-rel-simplify

Less automatical evaluation for Equality, improve simplification
Merge pull request #8213 from skirpichev/return-uneval-limit

Return Limit instance if limit function can't compute the limit
Merge pull request #8281 from hamishdickson/Master

Add new test to test_qubit and refactor test_qubit.py