(plot_2d_diagram): show_function using line/point for both continuous and discontinuous cases
raise UnimplementedError uncovered intervals are found, for discontinuous case
Add minimal_uncovered_interval_example()
Fix a bug when convered_intervals is empty
Add minimal_has_uncovered_interval() and rename minimal_no_covered_interval()
Fix a bug
make compatible with changes in functions.sage
Add bug example
Fix a doctest
Use Python module system for loading
Add many doctests
(extremality_test): In discontinuous case, bail out only after the finite dimensional test.  Better error message.
Merge branch 'master' into discontinuous_piecewise
Enable doctesting in bug_examples.  Add currently failing test.
Merge branch 'discontinuous_piecewise'