`wp_schedule_single_event()` should not prevent scheduling a future duplicate event. It should only reject an event as a duplicate if there is already a similar event scheduled within 10 minutes of the given timestamp.

Adds unit tests, fixes existing cron test.

Props tellyworth.

See [9181], #6966.
Fixes #28213.


git-svn-id: https://develop.svn.wordpress.org/trunk@29939 602fd350-edb4-49c9-b593-d223f7449a82
Overhaul SQL generating logic in WP_Meta_Query to avoid unnecessary table joins.

The logic used to generate clause SQL in `WP_Meta_Query` is somewhat arcane,
stemming mostly from an ongoing effort to eliminate costly table joins when
they are not necessary. By systematizing the process of looking for shareable
joins - as was done in `WP_Tax_Query` [29902] - it becomes possible to simplify
the construction of SQL queries in `get_sql_for_clause()`. Moreover, the
simplified logic is actually considerably better at identifying shareable
joins, such that certain uses of `WP_Meta_Query` will see joins reduced by 50%
or more.

Includes integration tests for a representative cross-section of the query
clause combinations that result in shared table aliases.

Props boonebgorges, sc0ttkclark.
See #24093.

git-svn-id: https://develop.svn.wordpress.org/trunk@29940 602fd350-edb4-49c9-b593-d223f7449a82
Bail from cleaning meta query clause when it's not an array.

Later isset() checks on string values were causing notices on PHP < 5.4.

Props jorbin.
See #29642.

git-svn-id: https://develop.svn.wordpress.org/trunk@29941 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: Fix hover and focus style for links in content with custom color schemes.

Props iamtakashi, fixes #29978.


git-svn-id: https://develop.svn.wordpress.org/trunk@29942 602fd350-edb4-49c9-b593-d223f7449a82
Run JSValidate on core themes JS

fixes #29968
props netweb


git-svn-id: https://develop.svn.wordpress.org/trunk@29943 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: Removing unused custom color controls.

Props cainm, fixes #29982 and #29959.



git-svn-id: https://develop.svn.wordpress.org/trunk@29944 602fd350-edb4-49c9-b593-d223f7449a82
Invalidate cache for child terms when parent term is deleted.

Props socki03.
Fixes #29911.

git-svn-id: https://develop.svn.wordpress.org/trunk@29945 602fd350-edb4-49c9-b593-d223f7449a82