Unserialize `get_metadata()` results when 'key' is omitted.

Props mattkeys, nacin.
Fixes #15030.

git-svn-id: https://develop.svn.wordpress.org/trunk@30115 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: Change version compare string to '4.1-alpha' to avoid an error for alpha and beta testers during development.

fixes #30137.

git-svn-id: https://develop.svn.wordpress.org/trunk@30116 602fd350-edb4-49c9-b593-d223f7449a82