Preserves spaces and generally creates more accurate, cleaner titles from filenames of uploaded media. Merge of [38615] to the 4.2 branch. Fixes #37989. Built from https://develop.svn.wordpress.org/branches/4.2@39714 git-svn-id: http://core.svn.wordpress.org/branches/4.2@39654 1a063a9b-81f0-0310-95a4-ce76da25c4cd