Adds Graph.treewidth()
Merge branch 'u/saraedum/ticket/14482' of http://trac.sagemath.org/sage into ticket/15191
Merge branch 'u/saraedum/ticket/15192' of http://trac.sagemath.org/sage into ticket/15191
Add quotient with remainder and euclidean degree tests to the category of euclidean domains

For such test methods, there has to be a canonical name for the euclidean
degree. Just calling it degree() is very confusing: in the context of Integers
or p-adics, this term does not make too much sense. Additionally, there could
already be a degree() for some elements which happens to be different from the
degree function of the euclidean domain.
Note, that I could not just set euclidean_degree=degree for polynomials because
polynomials (even with coefficients in a field) can have a parent where this is
not the euclidean degree (e.g. in a field K[x]/(f)).
Implement a non-trivial some_elements() for polynomial rings

Before this just returned a single element, the generator. This should probably
be extended much more but at least this makes tests by the category framework
not entirely trivial.
FiniteStateMachine.deepcopy: additional doctest

In order to make sure that the deepcopy mechanism
preserves the links between states and vertices,
added another doctest.
quick fix
quick fix for smooth triangles too
don't use __str__ or __repr__ for tachyon string representations
fix doctests
more doctest fixes
Merge branch 'develop' into ticket/15191-EuclideanDomains_tests

Conflicts:
	src/sage/categories/euclidean_domains.py
	src/sage/rings/polynomial/polynomial_quotient_ring.py
use verbose option to check that plots render successfully
Merge branch 'develop' into ticket/15191

Conflicts:
	src/sage/categories/euclidean_domains.py
Fixed doctests for euclidean_degree
euclidean_degree() is not defined for zero element

Note that it is not enough to check whether a.is_zero() and b.is_zero() since
euclidean rings such as the p-adics might contain actual zero divisors
FiniteStateMachine: fix one more occurrence of raise E, ... (cf. #15990)

introduced at the same time
FiniteStateMachine._latex_: replaced inefficient code

Previously, a O(n^3) code was used in latex; this is now
O(m). This resulted in a reordering of the output of _latex_,
so doctests had to be adapted.
FiniteStateMachine: rewritten code after #16067

When re-reading the resulting code, some simplifications were made.
Merge remote-tracking branch 'aau/fsm/deepcopy_doctest' into fsm/code-cleanup-post-16067