Remove compile-time dependency on doc-view.el

* org-docview.el (org-docview-store-link): Use expanded macro to get
current page.
(doc-view-goto-page, image-mode-window-get): Declare functions for
byte compiler.

doc-view mode is not available in Emacs22.  We need to use the
expanded form of the macro `doc-view-current-page' at compile-time.

lisp/org-docview.el

@@ -45,7 +45,10 @@
 
 
 (require 'org)
-(eval-when-compile (require 'doc-view))	; doc-view-current-page macro
+
+(declare-function doc-view-goto-page "ext:doc-view" (page))
+(declare-function image-mode-window-get "ext:image-mode"
+		  (prop &optional winprops))
 
 (autoload 'doc-view-goto-page "doc-view")
 
@@ -66,7 +69,7 @@
   (when (eq major-mode 'doc-view-mode)
     ;; This buffer is in doc-view-mode
     (let* ((path buffer-file-name)
-	   (page (doc-view-current-page))
+	   (page (image-mode-window-get 'page))
 	   (link (concat "docview:" path "::" (number-to-string page)))
 	   (description ""))
       (org-store-link-props