dot: heuristic to switch between circles and ellipses

* src/twaalgos/dotty.cc: Add an option (e) to force elliptic shape, and
a heuristic to choose between circle and ellipse by default.
* src/bin/common_aoutput.cc, src/bin/dstar2tgba.cc: Document 'e'.
* src/taalgos/dotty.cc: Ignore 'e'.
* wrap/python/spot.py (setup): Do not force circular states.  The
default should be fine.
* src/tests/det.test, src/tests/dstar.test, src/tests/monitor.test,
src/tests/neverclaimread.test, src/tests/readsave.test,
src/tests/sccdot.test, src/tests/tgbagraph.test: Adjust expected
results.
* NEWS: Adjust.

wrap/python/spot.py

@@ -48,7 +48,7 @@ def setup(**kwargs):
                                            kwargs.get('fillcolor', '#ffffaa'))
 
     bullets = 'B' if kwargs.get('bullets', True) else ''
-    d = 'rcf({})'.format(kwargs.get('font', 'Lato')) + bullets
+    d = 'rf({})'.format(kwargs.get('font', 'Lato')) + bullets
     os.environ['SPOT_DOTDEFAULT'] = d
 
 # Global BDD dict so that we do not have to create one in user code.