Merge pull request #2791 from smichr/2787

do not use None in factor_list
Merge pull request #2795 from skirpichev/gh2794

solve_univariate_inequality: don't assume that solve returns reals
merge with master
Merge pull request #2798 from smichr/auto

Auto
bool, relational: added as_set method

`as_set` is the inverse method for existing `as_relational`
method for sets. `as_set` converts a univariate boolean or
relational expression to real set.

Example:

In [1]: from sympy import And, Or

In [2]: from sympy.abc import x

In [3]: And(x<2, x>-2).as_set()
Out[3]: (-2, 2)

In [4]: (x**2 > 4).as_set()
Out[4]: (-oo, -2) U (2, oo)
tests pass, refactory in progress
wrapped lines longer than 80 chars
-> Fix a documentation issue
Address review comments
Allow the caller to specify the generator
Test that we can work with Exprs directly
Improved Documentation and added _eval_conjugate method to gammma
Added cross-references and references
Added _eval_conjugate to loggamma
eval_conjugate for lowergamma, uppergamma
Clean up documentation for Gamma functions
Fix evaluation of conjugates of incomplete gamma functions
Implement more special values for the polygamma function
Improve doc for gamma functions
Remove some functionality that breaks hyperexpand