Add support for toric varieties

[novoselt]

This patch is a part of the following series adding support for cones/fans and toric varieties to Sage:

Prerequisites:

#8675 - Remove AmbientSpace._constructor and fix consequences

#8682 - Improve AlgebraicScheme_subscheme.__init__ and AmbientSpace._validate

#8694 - Improve schemes printing and LaTeXing

#8934 - Trivial bug in computing faces of non-full-dimensional lattice polytopes

#8936 - Expose facet inequalities for lattice polytopes

#8941 - _latex_ and origin for lattice polytopes

Main patches adding new modules:

#8986 - Add support for convex rational polyhedral cones

#8987 - Add support for rational polyhedral fans

#8988 - Add support for toric varieties

#8989 - Add support for Fano toric varieties

Everything was tested on sage.math using sage-4.4.2.rc0.

Known issues:

• Applying patch for toric varieties leads to a doctest error in sage.symbolic.random_tests, which I don't quite understand, especially since this patch just adds a new module! The documentation of the failing function says "This function will often raise an error because it tries to create an erroneous expression." I am not sure if this means that its doctest may cause these errors.

• The last two patches show a doctest coverage error about TestSuite. This doctest does not work yet for other schemes and therefore should not be expected to work for these derived classes (and indeed - it does not work). According to

​http://groups.google.com/group/sage-devel/browse_thread/thread/a42ace80078373b4 this should not be an obstacle to include these patches.