Normalize 'user_id' and 'user_ID' values in wp_new_comment() before passing the comment data to 'preprocess_comment' filter.

props dkotter.
fixes #23231.
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git-svn-id: http://core.svn.wordpress.org/trunk@28714 1a063a9b-81f0-0310-95a4-ce76da25c4cd