The existing (and still default) behavior is for an app that uses a protected
resource that requires TCC permission (e.g., bluetooth) to crash if iTerm2 does
not have a reason string in its info.plist. I try to have all the reason
strings, so this is mostly not a problem, but Apple likes to add new ones all
the time, so it can be a problem.

Confusingly, disclaiming ownership of a child causes iTerm2 to be held
responsible for its behavior rather than the child just crashing.

In order to disclaim ownership you have to use posix_spawn instead of fork +
exec. But posix_spawn is broken for ttys, so you have to use fork + posix_spawn
along with the POSIX_SPAWN_SETEXEC flag, which makes posix_spawn act like exec.

To verify existing bug:

1. Remove the bluetooth reason string
2. Run the sample app in the aforementioned issue
3. It will crash

To test the fix:

1. Turn on Advanced > Disclaim ownership of children
2. Delete ~/Library/Application Support/iTerm2/iTermServer*
3. Kill all running iTermServer processes.
4. Relaunch iTerm2 to ensure the most up-to-date iTermServer is running.
5. Run the sample app in the aforementioned issue
6. Get a TCC request: "iTerm2.app" would like to access bluetooth

I have left this flag off by default to avoid introducing risk into the
forthcoming 3.5 release which already has more that enough risk. I don't think
it's terribly dangerous so once 3.5 settles down this can be flipped on in a
beta.