bug#21857: PATCH to show message after `package-install` installs successfully

[Ryan Olson]

When `package-install` function finishes successfully, this patch
(below) shows the message "Package `package-name` installed."  This
matches the message that is shown with the function `package-delete`.
I feel like this solves the primary issue: messaging.  After this
patch, the user should know that everything was a success.

*** package.el.orig 2020-01-17 10:11:48.000000000 -0700
--- package.el 2020-01-17 10:12:36.000000000 -0700
*************** to install it but still mark it as selec
*** 2076,2082 ****
                   (package-compute-transaction () (list (list pkg))))))
          (progn
            (package-download-transaction transaction)
!           (package--quickstart-maybe-refresh))
        (message "`%s' is already installed" name))))

  (defun package-strip-rcs-id (str)
--- 2076,2083 ----
                   (package-compute-transaction () (list (list pkg))))))
          (progn
            (package-download-transaction transaction)
!           (package--quickstart-maybe-refresh)
!           (message "Package `%s' installed." name))
        (message "`%s' is already installed" name))))

  (defun package-strip-rcs-id (str)