* lisp/emacs-lisp/package.el: Revert buffer after any operation

* lisp/emacs-lisp/package.el: Revert buffer after any operation

Call `package-menu--post-refresh' after any operation that changes
the package database (`package-install' and `package-delete').  To
avoid performance issues in large transactions, these functions
add `post-refresh' to `post-command-hook' instead of calling it
immediately.
(package-menu--mark-or-notify-upgrades): New function.
(list-packages): Add it to `package--post-download-archives-hook'.
(package-menu--post-refresh): Lose the upgrade-checking code, add
code to remove itself from `post-command-hook'.
(package-install, package-delete): Add it to `post-command-hook'.
(package-menu-execute): Don't call `package-menu--post-refresh'.