Add characters to be stripped or replaced in sanitize_title_with_dashes().

 * Replace times (multiplication sign) with x.
 * Strip low quotation marks and other curly quotes we don't already deal with.
props SergeyBiryukov. fixes #19820.



git-svn-id: https://core.svn.wordpress.org/trunk@20686 1a063a9b-81f0-0310-95a4-ce76da25c4cd