Extend backend-agnostic vc functionality

this commit adds a default keybinding for the vc-gutter hydra (leader-g
.) if both vc-gutter and hydra are enabled. It ensures that the various
vc-*-log-view-modes open up in emacs state, and it adds hg, svn and bzr
to the list of vc backends handled by git-gutter

modules/ui/vc-gutter/autoload.el

@@ -23,5 +23,12 @@
   ("m" git-gutter:mark-hunk)
   ("p" git-gutter:popup-hunk)
   ("R" git-gutter:set-start-revision)
-  ("q" nil :color blue)
-  ("Q" (git-gutter-mode -1) :color blue))
+  ("q"
+   (when (get-buffer git-gutter:popup-buffer)
+     (kill-buffer (get-buffer git-gutter:popup-buffer)))
+   :color blue)
+  ("Q"
+   (progn (git-gutter-mode -1)
+          (when (get-buffer git-gutter:popup-buffer)
+            (kill-buffer (get-buffer git-gutter:popup-buffer))))
+   :color blue))

modules/ui/vc-gutter/config.el

@@ -51,6 +51,7 @@ is deferred until the file is saved. Respects `git-gutter:disabled-modes'."
               (git-gutter-mode +1)
               (remove-hook 'after-save-hook #'+vc-gutter-init-maybe-h 'local)))))))
 
+  (setq git-gutter:handled-backends '(git hg svn bzr))
   ;; Disable in Org mode, as per
   ;; <https://github.com/syl20bnr/spacemacs/issues/10555> and
   ;; <https://github.com/syohex/emacs-git-gutter/issues/24>. Apparently, the