Hide tooltip when Emacs looses focus

Needs Emacs 24.4 to work.

See GH-6

flycheck-pos-tip.el

@@ -79,16 +79,19 @@ Uses `pos-tip-show' under the hood."
   "A minor mode to show Flycheck error messages in a popup."
   :global t
   :group 'flycheck
-  (if flycheck-pos-tip-mode
-      (progn
-        (setq flycheck-pos-tip-old-display-function
-              flycheck-display-errors-function
-              flycheck-display-errors-function
-              #'flycheck-pos-tip-error-messages)
-        (add-hook 'post-command-hook #'flycheck-pos-tip-hide))
-    (setq flycheck-display-errors-function
-          flycheck-pos-tip-old-display-function)
-    (remove-hook 'post-command-hook 'flycheck-pos-tip-hide)))
+  (let ((hooks '(post-command-hook focus-out-hook)))
+    (if flycheck-pos-tip-mode
+        (progn
+          (setq flycheck-pos-tip-old-display-function
+                flycheck-display-errors-function
+                flycheck-display-errors-function
+                #'flycheck-pos-tip-error-messages)
+          (dolist (hook hooks)
+            (add-hook hook #'flycheck-pos-tip-hide)))
+      (setq flycheck-display-errors-function
+            flycheck-pos-tip-old-display-function)
+      (dolist (hook hooks)
+        (remove-hook hook 'flycheck-pos-tip-hide)))))
 
 (provide 'flycheck-pos-tip)