…code version.

On FreeBSD I would like to remove dependency on libprocstat completely, and replace it with libkvm to be more like the other *BSD platforms in terms of linker dependencies. This pull request is our first move in that direction.

Replace libprocstat with libkvm in cmd

_pipe_sink was assigned after call_on_setup(), after limit_fd_::on_setup(),
but this was too late. It must be assigned earlier so that
executor::get_used_handles() can see it and prevent limit_handles from
closing the internal pipe for passing exec() errors from child to parent.

Fixes: 1a1d677
Closes: #202
Signed-off-by: Daniel Klauer <[email protected]>

This re-adds the close(source) call which already existed here before
commit caa7b2f. pipe_out already closes the source fd when redirecting
stdout or stderr, it was just missing when redirecting both at once.

The pipe fds must be closed after redirecting to avoid keeping the pipe
open unnecessarily, for example the parent may want to close their end of
the pipe.

Closes: #353
Signed-off-by: Daniel Klauer <[email protected]>

Signed-off-by: Daniel Klauer <[email protected]>