Add support for update hooks

Previously we had install hooks but no update hooks.

el-get-core.el

@@ -56,8 +56,8 @@ call for doing the named package action in the given method.")
   (and (el-get-method name :install) t))
 
 (defun* el-get-register-method (name &key install update remove
-                                     install-hook remove-hook compute-checksum
-                                     guess-website)
+                                     install-hook update-hook remove-hook
+                                     compute-checksum guess-website)
   "Register the method for backend NAME, with given functions"
   (let (method-def)
     (loop for required-arg in '(install update remove)
@@ -67,7 +67,7 @@ call for doing the named package action in the given method.")
                    (plist-put method-def
                               (intern (format ":%s" required-arg))
                               (symbol-value required-arg))))
-    (loop for optional-arg in '(install-hook remove-hook
+    (loop for optional-arg in '(install-hook update-hook remove-hook
                                 compute-checksum guess-website)
         if (symbol-value optional-arg)
         do (setq method-def

el-get.el

@@ -705,8 +705,13 @@ PACKAGE may be either a string or the corresponding symbol."
 (defun el-get-post-update (package)
   "Post update PACKAGE. This will get run by a sentinel."
   (let* ((sync el-get-default-process-sync)
-         (source   (el-get-package-def package))
+	 (type     (el-get-package-type package))
+	 (hooks    (el-get-method type :update-hook))
 	 (commands (el-get-build-commands package)))
+
+    ;; post-update is the right place to run update-hook
+    (run-hook-with-args hooks package)
+
     (el-get-build package commands nil sync 'el-get-post-update-build)))
 
 (defun el-get-update-requires-reinstall (package)