add signsimp to simplify.py

This should probably be part of symplify()'s procedure, right after

    original_expr = expr
    expr = signsimp(expr)

Any unevaluated Muls that were introduced that weren't changed are
restored to their original Add if they still remain after making
the substition. e.g. exp(y - x) -> exp(-(x - y)) is restored to
exp(y - x) if no change was effected. However, something like
exp((y - x)*(b - a)) ->-> exp((x - y)*(a - b)) does not have the
unevaluated Muls remaining so it there is nothing to change back.
use signsimp in simplify
signsimp watches for production of non-Basic expressions
simplify use of simplify flag in matrices

Cleaned up the use of simplify and simplified in matrices.py.

It's confusing to know which word to use to say you want to simplification to be used (and there was one test that had used the wrong keyword). The way I've done it now is to not have two keywords: set simplify to True if you want simplification (defaulting to sympy's simplify) or pass your own function to use that instead. There is no need for two words (simplified to use simplification, defaulting to sympy's simplify and simplify to define a different function). The use of simplified now raises a deprecation warning.

eigenvects now accepts a custom simplifier like the other matrix functions.
use signsimp in eigenvects
correct use of simplify flag in solve test
keep sympify from allowing autosimplification into Mul
remove use of real_root in checksol

The two solutions are now obtained; and no solution is found for the
test that formerly had the [1/3] as the solution (and that was confirmed
at WolframAlpha).
inferences raises an error on Number input

    Some atoms should raise an error (like Numbers) and others
    (like Symbols) should not. A commented-out test was uncommented.
Geometry: simplify coefficients
Merge pull request #1135 from smichr/3109c

3109c
Add Aleksandar Makelov to AUTHORS/aboutus.txt
Merge pull request #1157 from Krastanov/amakelov

Add Aleksandar Makelov to AUTHORS/aboutus.txt
Merge pull request #1152 from manoj2378/trigonometricFunctions

Improved trigonometric Functions
Fix entry in AUTHORS file
3099: try to speed up is_constant

- try substitution before evaluation - if different Rationals are obtained
then False can be returned.

- try evaluation with real before complex in is_constant

There is an issue with trying to evaluate a Sum with a subs keyword; an
issue (#3174) was opened for that and doctests that rely on it skipped
and an XFAIL test added.
Merge pull request #1134 from smichr/3099

3099: try to speed up is_constant
do not rely on is_real for comparable test

When foo.is_number and foo.is_real is used to determine whether
something is positive or negative there are two problems:

1) this discriminates against expressions for which is_real is None
2) this doesn't allow is_positive|negative to answer False for
   complex numbers -- they answer None at present

When evaluating is_real|integer, the presence of more than one
argument that does not have that attribute necessitates returning None
rather than False since those two properties may cancel out. A key
word to allow this option has been added to the
operations._eval_template_is_attr function.
Add a more helpful error message to the test for all classes in test_args.py
Merge pull request #1153 from smichr/assumptions

do not rely on is_real for comparable test