A better fix for #357.

This is a better fix for several reasons:

- It's more portable; the arguments/options to 'ps' vary widely across
  platforms.
- Killing children by forking yet more children (i.e., via backtick) is
  problematic when you're trying to kill processes because of resource
  starvation.
- Processes should not signal processes other than their own children,
  especially in a generic task-runner like Foreman. If the signal
  should propagate, then the sub-process should propagate signals to its
  children itself. There's no way to know what cleanup or preparation
  is necessary for a clean shutdown (e.g., SIGINT/SIGTERM), and
  in what order grandchild processes should be shut down to properly
  release locks, close files, etc.
- foreman-runner doesn't (shouldn't?) create grandchild processes; the
  last thing it does is `exec` the program it's launching, which
  will replace the program of the *current* process with the one
  being started up.

lib/foreman/engine.rb

@@ -176,19 +176,14 @@ class Foreman::Engine
   #
   # @param [String] signal  The signal to send to each process
   #
-  def kill_children(signal="SIGTERM")
-    if Foreman.windows?
-      @running.each do |pid, (process, index)|
-        system "sending #{signal} to #{name_for(pid)} at pid #{pid}"
-        begin
-          Process.kill(signal, pid)
-        rescue Errno::ESRCH, Errno::EPERM
-        end
-      end
-    else
+  def kill_children( signal="SIGTERM" )
+    @running.each do |pid, (process, index)|
+      system "sending #{signal} to #{name_for(pid)} at pid #{pid}"
       begin
-        Process.kill signal, *@running.keys unless @running.empty?
-      rescue Errno::ESRCH, Errno::EPERM
+        Process.kill( signal, pid )
+      rescue Errno::ESRCH, Errno::EPERM => err
+        system "  %p when sending signal %p to pid %d: %s" %
+          [ err.class, signal, pid, err.message ]
       end
     end
   end
@@ -198,14 +193,7 @@ class Foreman::Engine
   # @param [String] signal  The signal to send
   #
   def killall(signal="SIGTERM")
-    if Foreman.windows?
-      kill_children(signal)
-    else
-      begin
-        Process.kill "-#{signal}", Process.pid
-      rescue Errno::ESRCH, Errno::EPERM
-      end
-    end
+    kill_children(signal)
   end
 
   # Get the process formation