Add custom groups for VC backends, for consistency with vc-bzr.

Callers changed.

* vc/vc-arch.el (vc-arch):
* vc/vc-cvs.el (vc-cvs):
* vc/vc-git.el (vc-git):
* vc/vc-hg.el (vc-hg):
* vc/vc-mtn.el (vc-mtn):
* vc/vc-rcs.el (vc-rcs):
* vc/vc-sccs.el (vc-sccs):
* vc/vc-svn.el (vc-svn): New customization group.

Fixes: debbugs:10871

lisp/vc/vc-sccs.el

@@ -47,6 +47,11 @@
 ;;   :type '(repeat directory)
 ;;   :group 'vc)
 
+(defgroup vc-sccs nil
+  "VC SCCS backend."
+  :version "24.1"
+  :group 'vc)
+
 (defcustom vc-sccs-register-switches nil
   "Switches for registering a file in SCCS.
 A string or list of strings passed to the checkin program by
@@ -57,7 +62,7 @@ If t, use no switches."
 		 (string :tag "Argument String")
 		 (repeat :tag "Argument List" :value ("") string))
   :version "21.1"
-  :group 'vc)
+  :group 'vc-sccs)
 
 (defcustom vc-sccs-diff-switches nil
   "String or list of strings specifying switches for SCCS diff under VC.
@@ -67,13 +72,13 @@ If nil, use the value of `vc-diff-switches'.  If t, use no switches."
 		 (string :tag "Argument String")
 		 (repeat :tag "Argument List" :value ("") string))
   :version "21.1"
-  :group 'vc)
+  :group 'vc-sccs)
 
 (defcustom vc-sccs-header '("%W%")
   "Header keywords to be inserted by `vc-insert-headers'."
   :type '(repeat string)
   :version "24.1"     ; no longer consult the obsolete vc-header-alist
-  :group 'vc)
+  :group 'vc-sccs)
 
 ;;;###autoload
 (defcustom vc-sccs-master-templates
@@ -86,7 +91,7 @@ For a description of possible values, see `vc-check-master-templates'."
 			 (choice string
 				 function)))
   :version "21.1"
-  :group 'vc)
+  :group 'vc-sccs)
 
 
 ;;;