org-table.el: Fix bug: make sure references to $0 are correctly handled.

* org-table.el (org-table-get-range): Fix bug: make sure
references to $0 are correctly handled.

Thanks to Nick Dokos for the suggestion.

This fixes the computation of values in this table:

| Record   |        Slope |    ConfLower |    ConfUpper |
|----------+--------------+--------------+--------------|
| GISTEMP  | 0.0173837600 | 0.0133209130 | 0.0214466060 |
| HadCrut3 | 0.0158602890 | 0.0118664610 | 0.0198541180 |

See this message/thread:
http://article.gmane.org/gmane.emacs.orgmode/54341

lisp/org-table.el

@@ -2663,8 +2663,8 @@ in the buffer and column1 and column2 are table column numbers."
 ;      (setq r2 (or r2 r1) c2 (or c2 c1))
       (if (not r1) (setq r1 thisline))
       (if (not r2) (setq r2 thisline))
-      (if (not c1) (setq c1 col))
-      (if (not c2) (setq c2 col))
+      (if (or (not c1) (= 0 c1)) (setq c1 col))
+      (if (or (not c2) (= 0 c2)) (setq c2 col))
       (if (and (not corners-only)
 	       (or (not rangep) (and (= r1 r2) (= c1 c2))))
 	  ;; just one field