new copyright; att/bsd/shared

fix :r breakpoint-skipping code; simplify; comment

mr-frog reminded me: need to invalidate ptrace cache
when subprocess runs. how did I ever forget?

simplify: starting new process is like restarting old,
since setup() fishes out the start PC; junk the `new process' flag.
Fix starting with single step: exect() works only on VAX, execve()
works eve

simplify: starting new process is like restarting old,
since setup() fishes out the start PC; junk the `new process' flag.
Fix starting with single step: exect() works only on VAX, execve()
works everywhere.

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:s on new process should not decrement run count

new version from Chris Torek