Search Builder: Contact created_date and modified_date filters not working

Contact/BAO/Query.php contains special handling for most date fields (birth_date, deceased_date, etc.). This is missing for created_date and modified_date. Without this, the resulting query adds a LOWER statement on the date string which causes it to return 0 rows in all cases.

— Original post —
In 4.6.0 the Javascript date picker provides the wrong format for MySQL. Either Javascript needs to output the date in the format 2015-05-07 or the process receiving it needs to reinterpret "20150507" to "2015-05-07".