add absolute order
trac 14816 cleanup patch
trac #14816 minor details
Merge branch 'u/chapoton/14816' of trac.sagemath.org:sage into public/combinat/absolute_order-14816
Refactored into the appropriate categories.
Merge branch 'develop' into public/combinat/absolute_order-14816
trac #11840 first step, plus doc python 3 and trac role cleanup
trac #11840 details, making sure that tests pass
trac #11840 swapped two lines
Typesetting errors in docstring of FiniteStateMachine._latex_transition_label_

{{{''}}} was used instead of {{{``}}} in {{{FiniteStateMachine._latex_transition_label_}}},
{{{Automaton._latex_transition_label_}}}, {{{Transducer._latex_transition_label_}}}.

In the latter, an {{{EXAMPLES::}}} was also missing.
changed latex-output of multi-character variables to \mathit{...}

See Trac #15870.
latex_variable_name('') now returns '' instead of '\\mathit{}' (or '\\mbox{}' in the old code)
inserted doctests for \mathit in infinite_polynomial_ring
salvaging docs, doctests and (in one case) functionality from deprecata removed in #15466
fix own blunders
Merge branch 'u/chapoton/11840' of trac.sagemath.org:sage into 11840

Conflicts:
	src/sage/symbolic/expression.pyx
Merge branch 'public/combinat/absolute_order-14816' of trac.sagemath.org:sage into public/combinat/absolute_order-14816

* 'public/combinat/absolute_order-14816' of trac.sagemath.org:sage:
  Refactored into the appropriate categories.
  trac #14816 minor details
  trac 14816 cleanup patch
  add absolute order
added ast, bullet, circ, times, star to common_varnames

Therefore, the mentioned symbols are displayed correctly when using latex(...)
simplified _latex_ of infinite_polynomial_ring; it now uses latex_variable_name
doctest for trac #15870 added