Add plugin_action_links_{$plugin} hook

[strider72]

Per discussion on wp-hackers, this is a patch to add a plugin_action_links_{$plugin} filter.

It runs just after the plugin_action_links filter.

Note -- the initial patch on this uses the plugin_basename for $plugin, rather than the string returned from add_options_page.

adds plugin_action_links_{$plugin} filter to plugins.php

Nice!

New patch = old patch plus after_plugin_row_{$plugin} filter. Two birds with one stone?

New patch has one other difference -- I added $plugin_data back into the plugin_action_links_{$plugin} filter.

I had removed it in the first patch, but it should probably be there -- no real reason to remove it.

As a demonstration, this patch modifies Akismet to use this new filter. Now has "Settings" link in plugin admin row.

(In [9124]) Add some plugin specific hooks to the plugin management screen. Fixes #7856 props strider72.