Added docstring to lambdified functions

If arguments have names, that is used. Otherwise the stack is inspected
to determine if the name can be inferred *with certainty*. If there is
more than one variable pointing to the object, then the name cannot be
determined with certainty, and 'arg_#', where '#' is the number of the
arg is used.
Vector pretty print test fix. Fixes issue #7679.
pretty_symbology: Don't assume the output of U() is not None

U() returns None when unicodedata can't be imported. I'm not sure how to test
this because it's only reproducible if unicodedata from the standard library
can't be imported.  I suppose we could add a hook to test it. It won't be
straight-forward though because the key thing is to make sure it works
correctly at import time.

Fixes #8163.
Return Limit instance if limit function can't compute the limit

Before: PoleError exception was raised
Merge remote-tracking branch 'upstream/master' into lambdify_docstring

Conflicts:
	sympy/utilities/lambdify.py
Use workprec context manager to temporary change mpmath binary precision
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
Merge pull request #8268 from skirpichev/use-workprec

Use workprec context manager to temporary change mpmath binary precision
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