Remove old magit override on init

The old magit override was too broad. And now magit is switching to use
ido-ubiquitous, So users who have customized their overrides will not
have the old override auto-removed when they update, and magit could end
up stuck with no ido completion. So the init code now handles this
migration for the user and prompts them via warning to save the fix.

ido-ubiquitous.el

@@ -301,7 +301,7 @@ using overrides and disable it for everything else."
     ;; https://github.com/DarwinAwardWinner/ido-ubiquitous/issues/28
     (enable regexp "\\`\\(find\\|load\\|locate\\)-library\\'")
     ;; https://github.com/DarwinAwardWinner/ido-ubiquitous/issues/37
-    ;; Org and Magit already support ido natively
+    ;; Org already supports ido natively
     (disable prefix "org-")
     ;; https://github.com/bbatsov/prelude/issues/488
     ;; https://github.com/DarwinAwardWinner/ido-ubiquitous/issues/44
@@ -927,17 +927,46 @@ Debug info is printed to the *Messages* buffer."
   :global t
   :group 'ido-ubiquitous)
 
-(defun ido-ubiquitous-initialize ()
-  "Do initial setup for ido-ubiquitous.
-
-This only needs to be called once when the file is first loaded."
+(defsubst ido-ubiquitous--fixup-old-advice ()
   ;; Clean up old versions of ido-ubiquitous advice if they exist
   (ignore-errors (ad-remove-advice 'completing-read 'around 'ido-ubiquitous))
   (ignore-errors (ad-remove-advice 'ido-completing-read 'around 'detect-replacing-cr))
   (ignore-errors (ad-remove-advice 'ido-magic-forward-char 'before 'ido-ubiquitous-fallback))
   (ignore-errors (ad-remove-advice 'ido-magic-backward-char 'before 'ido-ubiquitous-fallback))
   (ignore-errors (ad-remove-advice 'ido-exit-minibuffer 'around 'compatibility))
-  (ad-activate-all)
+  (ad-activate-all))
+
+(defsubst ido-ubiquitous--fixup-old-magit-overrides ()
+  (let ((old-override '(disable prefix "magit-"))
+        (new-override '(disable exact "magit-builtin-completing-read")))
+    (when (member old-override
+                  ido-ubiquitous-command-overrides)
+      (customize-set-variable
+       'ido-ubiquitous-command-overrides
+       (remove old-override ido-ubiquitous-command-overrides))
+      (unless (member new-override ido-ubiquitous-function-overrides)
+        (customize-set-variable 'ido-ubiquitous-function-overrides
+                                (append ido-ubiquitous-function-overrides
+                                        (list new-override))))
+      (display-warning
+       'ido-ubiquitous
+       "Fixing obsolete magit overrides.
+
+Magit has changed recently such that the old override that
+ido-ubiquitous defined for it now causes problems. This old
+override has been automatically removed and the new one added.
+Please use `M-x customize-group ido-ubiquitous' and review the
+override variables and save them to your customization file."
+       :warning))))
+
+(defun ido-ubiquitous-initialize ()
+  "Do initial setup for ido-ubiquitous.
+
+This only needs to be called once when the file is first loaded.
+It cleans up any traces of old versions of ido-ubiquitous and
+then sets up the mode."
+  (ido-ubiquitous--fixup-old-advice)
+  (ido-ubiquitous--fixup-old-magit-overrides)
   ;; Make sure the mode is turned on/off as specified by the value of
   ;; the mode variable
   (ido-ubiquitous-mode (if ido-ubiquitous-mode 1 0)))