Update license manager submodule
Added boolean return statements to image_output function.
added WPSEO_Twitter method tests, cleaned up unnecessary ob_clean statements.
add missing text domain to third-party plugin related notices
Merge pull request #1050 from dannyvankooten/bugfix/add-text-domain

add missing text domain to third-party plugin related notices
Merge branch 'master' of git://github.com/Yoast/wordpress-seo into Issue-1032-sample-permalink