Makefile default to notests for users

Users see failing tests and complain. Some tests are intended to fail.
These can be enabled from the command line, e.g.
   make TESTSET=regresstests

The available options are
richtests      -- the Albert Rich integration tests (very long time)
catstests      -- the computer algebra test suite CATS (very long time)
regresstests   -- the src/input and algebra tests (normal)
alltests       -- very long time
notests        -- skip the tests