Add a `user_new_form` hook, with context. props johnjamesjacoby, strangerstudios, jeremyfelt, DrewAPicture. fixes #18709.


git-svn-id: http://develop.svn.wordpress.org/trunk@25629 602fd350-edb4-49c9-b593-d223f7449a82
Inline documentation for hooks in wp-admin/includes/class-wp-plugin-install-list-table.php.

Props naomicbush.
Fixes #25357.


git-svn-id: http://develop.svn.wordpress.org/trunk@25630 602fd350-edb4-49c9-b593-d223f7449a82