Add unit test cases for message meta.

See #3083.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9186 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Fix oEmbed in private messages.

oEmbed caching for private messages will be in the next commit.

See #5990.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9187 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Messages: Add oEmbed caching.

With the introduction of the messages meta table (#3083), we are now able
to cache oEmbed responses.  On subsequent fetches, we will now reference
the message cache instead of pinging the oEmbed provider.

This mirrors our functionality with BP's activity implementation of oEmbed.

See #5990.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9188 cdf35c40-ae34-48e0-9cc9-0c9da1808c22