dot: make "a" the default

Fixes #319.

* spot/twaalgos/dot.cc: Enable "a" by default.
* bin/common_aoutput.cc, NEWS: Document it.
* doc/org/autfilt.org, doc/org/concepts.org, doc/org/dstar2tgba.org,
doc/org/hierarchy.org, doc/org/ltl2tgba.org, doc/org/oaut.org,
doc/org/randaut.org, doc/org/satmin.org, doc/org/tut23.org,
doc/org/tut24.org, doc/org/tut30.org, doc/org/tut31.org: Adjust or
simplify the documentation.
* tests/core/det.test, tests/core/dstar.test, tests/core/monitor.test,
tests/core/neverclaimread.test, tests/core/readsave.test,
tests/core/tgbagraph.test, tests/core/wdba.test,
tests/python/_autparserr.ipynb, tests/python/automata-io.ipynb,
tests/python/automata.ipynb, tests/python/highlighting.ipynb
tests/python/ltsmin-dve.ipynb, tests/python/ltsmin-pml.ipynb,
tests/python/product.ipynb, tests/python/testingaut.ipynb,
tests/python/word.ipynb: Adjust test cases.

NEWS

@@ -2,6 +2,13 @@ New in spot 2.5.1.dev (not yet released)
 
   Library:
 
+  - Option "a" of print_dot(), for printing the acceptance condition,
+    is now enabled by default.  Option "A", introduced in Spot 2.4,
+    can be used to hide the acceptance condition in case you do not
+    want it.  This change of course affects the --dot option of all
+    the command-line tools, as well as the various way to display
+    automata using the Python bindings.
+
   - cleanup_parity() and cleanup_parity_here() are smarter and now
     remove from the acceptance condition the parity colors that are
     not used in the automaton.