Fixes <rdar://problem/3976872> REGRESSION (Mail): Pasted lines of plain text don't get the proper style if pasted into newlines

        For style matched paste, style information was gathered incorrectly.

        Test cases added:
        * layout-tests/editing/pasteboard/3976872-expected.txt: Added.
        * layout-tests/editing/pasteboard/3976872.html: Added.

        * khtml/editing/replace_selection_command.cpp:
        (khtml::ReplaceSelectionCommand::doApply):
        Even though the startBlock (selection.start().node()->enclosingBlockFlowElement) is where manipulation
        begins on a paste, it can be missing necessary style information.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@10478 268f45cc-cd09-0410-ab3c-d52691b4dbfc