patch 9.0.0734: cursor position invalid when scrolling with 'smoothscroll'

Problem:    Cursor position invalid when scrolling with 'smoothscroll' set.
            (Ernie Rael)
Solution:   Add w_valid_skipcol and clear flags when it changes.  Adjust
            w_skipcol after moving the cursor.
diff --git a/src/proto/move.pro b/src/proto/move.pro
index de8bf51..07a70d2 100644
--- a/src/proto/move.pro
+++ b/src/proto/move.pro
@@ -35,6 +35,7 @@
 void f_virtcol2col(typval_T *argvars, typval_T *rettv);
 void scrolldown(long line_count, int byfold);
 void scrollup(long line_count, int byfold);
+void adjust_skipcol(void);
 void check_topfill(win_T *wp, int down);
 void scrolldown_clamp(void);
 void scrollup_clamp(void);