Revert "Tweak to keep Valgrind happy with tree/type allocation changes"

This reverts commit a6bf912d54fe70dd50d45cc854124a1fb613e3e1.
Revert "Same allocation scheme for types"

This reverts commit 64ae2e51b4a0ce305a96ee690cb1310d767bba37.
Revert "Simplify tree allocation scheme"

This reverts commit abd7938846a728fa2fac293c25f024e4972372c5.
Remove unnecessary malloc
Improve Valgrind leak check in run_regr.rb
Improve handling of fatal errors in interactive mode
Make "run" command synchronous
Add interactive startup banner
Generate "help" output automatically
Now "run" command warns if there are no future events