ob-core, ob-exp, ob-haskell, ob-python: declarations for org-src-preserve-indentations

* lisp/ob-core.el: Add comment to forward declaration of
  'org-src-preserve-indentations'.
* lisp/ob-exp.el: Require org-src to import
  'org-src-preserve-indentations'.
* lisp/ob-haskell.el, lisp/ob-python.el: Remove superfluous forward
  declaration of 'org-src-preserve-indentations', since it gets
  imported by other requires.

lisp/ob-core.el

@@ -1349,7 +1349,7 @@ specified in the properties of the current outline entry."
 	  (org-entry-get org-babel-current-src-block-location
 			 (concat "header-args:" lang) 'inherit))))))
 
-(defvar org-src-preserve-indentation)
+(defvar org-src-preserve-indentation) ;; declare defcustom from org-src
 (defun org-babel-parse-src-block-match ()
   "Parse the results from a match of the `org-babel-src-block-regexp'."
   (let* ((block-indentation (length (match-string 1)))

lisp/ob-exp.el

@@ -24,6 +24,7 @@
 
 ;;; Code:
 (require 'ob-core)
+(require 'org-src)
 (eval-when-compile
   (require 'cl))
 

lisp/ob-haskell.el

@@ -147,7 +147,6 @@ specifying a variable of the same value."
       (concat "[" (mapconcat #'org-babel-haskell-var-to-haskell var ", ") "]")
     (format "%S" var)))
 
-(defvar org-src-preserve-indentation)
 (defvar org-export-copy-to-kill-ring)
 (declare-function org-export-to-file "ox"
 		  (backend file

lisp/ob-python.el

@@ -56,8 +56,6 @@ This will typically be either 'python or 'python-mode."
   :package-version '(Org . "8.0")
   :type 'symbol)
 
-(defvar org-src-preserve-indentation)
-
 (defcustom org-babel-python-hline-to "None"
   "Replace hlines in incoming tables with this when translating to python."
   :group 'org-babel