Makefile: SKIP_EXAMPLES=1 to skip running ./examples
Makefile: SKIP_EXAMPLES=1 to skip running ./examples

Also make examples run only when when 'examples' has changed.

We were forcing ourselves to confront the slowness of ncc0. But we get
it.

nanocritical/n,nanocritical/n,nanocritical/n,nanocritical/n