Change Guard::Interactor#lock and #unlock methods so they will lock interactor

in the right thread and free $stdin [closes #137].

lib/guard/interactor.rb

@@ -1,6 +1,9 @@
 module Guard
   class Interactor
 
+    class LockException < Exception; end
+    class UnlockException < Exception; end
+
     attr_reader :locked
 
     def initialize
@@ -11,7 +14,8 @@ module Guard
       return if ENV["GUARD_ENV"] == 'test'
       @thread = Thread.new do
         loop do
-          if (entry = $stdin.gets) && !@locked
+          begin
+            if !@locked && (entry = $stdin.gets)
               entry.gsub! /\n/, ''
               case entry
               when 'stop', 'quit', 'exit', 's', 'q', 'e'
@@ -24,22 +28,29 @@ module Guard
                 ::Guard.run_all
               end
             end
+          rescue LockException
+            lock
+          rescue UnlockException
+            unlock
           end
         end
       end
-
-    def stop
-      @thread.kill
     end
 
     def lock
+      if @thread == Thread.current
         @locked = true
-      stop
+      else
+        @thread.raise(LockException)
+      end
     end
 
     def unlock
+      if @thread == Thread.current
         @locked = false
-      start
+      else
+        @thread.raise(UnlockException)
+      end
     end
 
   end