Fix some compiler warnings

* lisp/ob.el (org-src-lang-modes): Defvar.
(org-at-item-p): Declare function.
* lisp/ob-calc.el (calc-store): Require.
(var-syms): Defvar.
* lisp/ob-python.el (py-default-interpreter): Defvar.

lisp/ob-calc.el

@@ -29,6 +29,7 @@
 ;;; Code:
 (require 'ob)
 (require 'calc)
+(require 'calc-store)
 (unless (featurep 'xemacs) (require 'calc-trail))
 (eval-when-compile (require 'ob-comint))
 
@@ -83,6 +84,7 @@
     (with-current-buffer (get-buffer "*Calculator*")
       (calc-eval (calc-top 1)))))
 
+(defvar var-syms) ; Dynamically scoped from org-babel-execute:calc
 (defun ob-calc-maybe-resolve-var (el)
   (if (consp el)
       (if (and (equal 'var (car el)) (member (cadr el) var-syms))

lisp/ob-python.el

@@ -130,6 +130,7 @@ Emacs-lisp table, otherwise return the results as a string."
   "Return the buffer associated with SESSION."
   (cdr (assoc session org-babel-python-buffers)))
 
+(defvar py-default-interpreter)
 (defun org-babel-python-initiate-session-by-key (&optional session)
   "Initiate a python session.
 If there is not a current inferior-process-buffer in SESSION

lisp/ob.el

@@ -35,6 +35,7 @@
 (require 'org-macs)
 
 (defvar org-babel-call-process-region-original)
+(defvar org-src-lang-modes)
 (declare-function show-all "outline" ())
 (declare-function tramp-compat-make-temp-file "tramp-compat"
                   (filename &optional dir-flag))
@@ -74,6 +75,7 @@
 (declare-function org-babel-lob-execute-maybe "ob-lob" ())
 (declare-function org-number-sequence "org-compat" (from &optional to inc))
 (declare-function org-in-item-p "org-list" ())
+(declare-function org-at-item-p "org-list" ())
 (declare-function org-list-parse-list "org-list" (&optional delete))
 (declare-function org-list-to-generic "org-list" (LIST PARAMS))
 (declare-function org-list-struct "org-list" ())