[New sniff] Do not load WordPress core files directly about wpthemereview

[selul]

@grappler i would like to work on this one.

[selul]

i will pass this to @dmtrmrv who is working on #44 as this issue is a simple extending to the one he is working

[justintadlock]

Here's a list of files that I can think of that some themes might need to include and why:

• wp-admin/includes/plugin.php - For use of is_plugin_active() to check if a plugin is active.
• wp-admin/includes/plugin-install.php - For use of plugins_api() to list recommended plugins.
• wp-admin/includes/theme.php - For use of themes_api() to list child themes.

[dingo-d]

@selul Any news on this one?