Fix bug #2749 with overflow-newline-into-fringe in visual-line-mode.

Fix bug #2749 with overflow-newline-into-fringe in visual-line-mode.

 src/xdisp.c (IT_OVERFLOW_NEWLINE_INTO_FRINGE): Don't disallow
 word-wrap, so that overflow-newline-into-fringe would work in
 visual-line-mode.
 (move_it_in_display_line_to): When the last scanned display
 element fits exactly on the display line, and
 overflow-newline-into-fringe is non-nil, but wrap_it is valid,
 don't return MOVE_NEWLINE_OR_CR, but instead back up to the last
 wrap point and return MOVE_LINE_CONTINUED.  Fixes problems with
 finding buffer position that corresponds to pixel coordinates,
 e.g. in buffer_posn_from_coords.