org-crypt.el: Fix warning

* org-crypt.el (org-encrypt-string, org-encrypt-entry)
(org-decrypt-entry): Fix warning.

TINYCHANGE

epg-context is let-bounded in org-crypt and then epg local set it in
this context.  It should just be set as local var instead of being let
bounded.

See http://debbugs.gnu.org/cgi/bugreport.cgi?bug=15081

lisp/org-crypt.el

@@ -161,8 +161,8 @@ See `org-crypt-disable-auto-save'."
   (if (and (string= crypt-key (get-text-property 0 'org-crypt-key str))
 	   (string= (sha1 str) (get-text-property 0 'org-crypt-checksum str)))
       (get-text-property 0 'org-crypt-text str)
-    (let ((epg-context (epg-make-context nil t t)))
-      (epg-encrypt-string epg-context str (epg-list-keys epg-context crypt-key)))))
+      (set (make-local-variable 'epg-context) (epg-make-context nil t t))
+    (epg-encrypt-string epg-context str (epg-list-keys epg-context crypt-key))))
 
 (defun org-encrypt-entry ()
   "Encrypt the content of the current headline."
@@ -170,11 +170,11 @@ See `org-crypt-disable-auto-save'."
   (require 'epg)
   (save-excursion
     (org-back-to-heading t)
+    (set (make-local-variable 'epg-context) (epg-make-context nil t t))
     (let ((start-heading (point)))
       (forward-line)
       (when (not (looking-at "-----BEGIN PGP MESSAGE-----"))
         (let ((folded (outline-invisible-p))
-              (epg-context (epg-make-context nil t t))
               (crypt-key (org-crypt-key-for-heading))
               (beg (point))
               end encrypted-text)
@@ -206,11 +206,11 @@ See `org-crypt-disable-auto-save'."
 	(forward-line)
 	(when (looking-at "-----BEGIN PGP MESSAGE-----")
 	  (org-crypt-check-auto-save)
+          (set (make-local-variable 'epg-context) (epg-make-context nil t t))
 	  (let* ((end (save-excursion
 			(search-forward "-----END PGP MESSAGE-----")
 			(forward-line)
 			(point)))
-		 (epg-context (epg-make-context nil t t))
 		 (encrypted-text (buffer-substring-no-properties (point) end))
 		 (decrypted-text
 		  (decode-coding-string