Use / or \ in textplot if the function is increasing or decreasing

Before:

0.99845 |                                      ... ....
        |                                    ..        ..
        |                                   .            .
        |                                  .              .
        |                                 .                .
        |                                .                  .
        |                               .                    .
        | .                            .                      .
5.55112 | -.--------------------------.------------------------.-
        |   .                        .                          .
        |    .                      .
        |     .                    .
        |      .                  .
        |       .                .
        |        .              .
        |         .            .
        |          ..        ..
-0.9984 |            ........
          -10                    0                          10

After:

0.99845 |                                      ... ....
        |                                    ..        ..
        |                                   /            \
        |                                  /              \
        |                                 /                \
        |                                /                  \
        |                               /                    \
        | \                            /                      \
5.55112 | -\--------------------------/------------------------\-
        |   \                        /                          \
        |    \                      /
        |     \                    /
        |      \                  /
        |       \                /
        |        \              /
        |         \            /
        |          ..        ..
-0.9984 |            ........
          -10                    0                          10
add support for algebraic functions in minpoly
fix test failures
add tests for minpoly over fraction fields
Fix bug in _choose_factor
minpoly: check that the variable is not contained in the ground domain
minpoly: fix test failures
minpoly: add support for algebraic extensions of QQ
minpoly: update documentation

also rename _minpoly_op_algebraic_number to _minpoly_op_algebraic_element
and update error messages
minpoly: add more tests
minpoly: fix doctest error
Improve subs for Derivative.

Perform substitutions if derivative variables are in a different, but
equivalent order and perform substitutions for subderivatives.
Add additional tests for Derivative subs method.
Report test name in case of runtest failure; add missing print_function.

Make runtests.py report the name of a test if an exception is thrown
before it outputs the test name normally. This makes sure that the
name of a test is printed even in the face of runtest machinery failure.

Added a print_function import from __future__ to test_codegen, which
would make tests fail all over the place when --enhance-asserts was
active.
Writing the RootSystem class
Merge remote-tracking branch 'sympy/master' into derivsubs

Conflicts:
	sympy/core/function.py
Made the following changes
1] Added ode_1st_power_series for first order differential equations
Adding more functionality to RootSystem
Updating classes to use __new__ instead of init
Fixing some doctest errors