Mac: Cmd+q appears to quit APL but can leave "invisible" background process running.

# RIDE Issue Report

### Describe the issue you are having
If an APL process is looping, typing Cmd+q, or the equivalent using the Force Quit ... menu, kills the session window but leaves a dyalog process running.

### Did you connect to an already running interpreter or start the interpreter from RIDE?
No

### How do you reproduce the issue?
{∇⍵}0 ⍝ hangs.
Now type Cmd+q ... Quit Dyalog APL. Are you sure? Yes
The application appears to quit and disappears from the ->Force Quit... list of running applications. However, the dyalog process continues to run, using 100% of a core.

### Paste the contents of Help → About (Shift+F1)
IDE:
Version: 4.0.2749
Platform: MacIntel
Date: 2017-03-17 13:59:13 +0000
Git commit: f75e3cf19b54ab6a231f74ed1ec4d7ad7bdae3b3
Preferences:{
"lineNums":"0",
"zoom":"7"
}

Interpreter:
Version: 16.0.29523
Platform: Mac-64
Edition: Unicode/64
Date: Mar 19 2017 at 02:32:01