Updating the 'class-metabox.php'

I needed to add a variable on this filter to allow the developer to know what post is been requested, instead of just the post content.
Merge pull request #239 from tudoparawp/master

Updating the 'class-metabox.php'
Add option to disable slug stop word cleaning
Add $post to all instances of `wpseo_pre_analysis_post_content` filter
Move help on Titles & Metas admin page to help tab
Updated translations

Updated de_DE, fa_IR, fi, hu_HU, it_IT, pl_PL, sv_SE and tr_TK
* Fix for compatibility with NextGen Gallery.
* bump to 1.4.16
Fixes comment of @GaryJones on [this commit](https://github.com/Yoast/wordpress-seo/commit/70b42d471427d53e1befe422b6251db7d0fc21d8)
Really fix stop words cleaning this time and move to 1.4.17
No longer unset shutdown hook as that breaks caching plugins.
Push 1.4.18.
Portuguese translation is now 100%
Switch to new newsletter system.
* Updated newsletter subscription form to reflect new newsletter system.
* Documentation
	* Updated readme.txt to reflect support changes.
	* Moved old sections of changelog to external file.
Fix typo
Move all rewrite flushing to shutdown, so it doesn't break other plugins who add their rewrites late.
Up version number to allow testing of previous fix.
Allow changing of post length requirements.
Add post_type to $job so it can be passed along and used in filters.
Turn the statistics object into a global instead of throwing it around all the time.
Use the term description for the OpenGraph description, if there is one.
Refactor OpenGraph class to use one internal function `og_tag` for output.
Add support for OpenGraph publication date, last modified date, tags and categories, mostly because [Pinterest added support for article tags](http://blog.pinterest.com/post/62158724907/find-and-save-great-reads-with-new-article-pins).
Prevent outputting `[&hellip;]` by replacing it with `&hellip;`
Add upload for Facebook image to Social tab.
Rename `objectL10n` to `wpseoL10n`, fixes #263.
Fix `og:sitename`, should be `go:site_name`.