patch 7.4.1611
Problem:    The versplit feature makes the code uneccessary complicated.
Solution:   Remove FEAT_VERTSPLIT, always support vertical splits when
            FEAT_WINDOWS is defined.
diff --git a/src/ui.c b/src/ui.c
index a7c9064..f686138 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -2583,7 +2583,7 @@
     int		which_button)	/* MOUSE_LEFT, MOUSE_RIGHT, MOUSE_MIDDLE */
 {
     static int	on_status_line = 0;	/* #lines below bottom of window */
-#ifdef FEAT_VERTSPLIT
+#ifdef FEAT_WINDOWS
     static int	on_sep_line = 0;	/* on separator right of window */
 #endif
     static int	prev_row = -1;
@@ -2623,7 +2623,7 @@
 	 * line, stop Visual mode */
 	if (on_status_line)
 	    return IN_STATUS_LINE;
-#ifdef FEAT_VERTSPLIT
+#ifdef FEAT_WINDOWS
 	if (on_sep_line)
 	    return IN_SEP_LINE;
 #endif
@@ -2681,7 +2681,7 @@
 	}
 	else
 	    on_status_line = 0;
-#ifdef FEAT_VERTSPLIT
+#ifdef FEAT_WINDOWS
 	if (col >= wp->w_width)		/* In separator line */
 	{
 	    on_sep_line = col - wp->w_width + 1;
@@ -2706,7 +2706,7 @@
 	if (VIsual_active
 		&& (wp->w_buffer != curwin->w_buffer
 		    || (!on_status_line
-#ifdef FEAT_VERTSPLIT
+#ifdef FEAT_WINDOWS
 			&& !on_sep_line
 #endif
 #ifdef FEAT_FOLDING
@@ -2730,9 +2730,7 @@
 	{
 	    /* A click outside the command-line window: Use modeless
 	     * selection if possible.  Allow dragging the status lines. */
-# ifdef FEAT_VERTSPLIT
 	    on_sep_line = 0;
-# endif
 # ifdef FEAT_CLIPBOARD
 	    if (on_status_line)
 		return IN_STATUS_LINE;
@@ -2764,7 +2762,7 @@
 	    else
 		return IN_STATUS_LINE | CURSOR_MOVED;
 	}
-#ifdef FEAT_VERTSPLIT
+#ifdef FEAT_WINDOWS
 	if (on_sep_line)			/* In (or below) status line */
 	{
 	    /* Don't use start_arrow() if we're in the same window */
@@ -2798,7 +2796,7 @@
 #endif
 	return IN_STATUS_LINE;			/* Cursor didn't move */
     }
-#ifdef FEAT_VERTSPLIT
+#ifdef FEAT_WINDOWS
     else if (on_sep_line && which_button == MOUSE_LEFT)
     {
 	if (dragwin != NULL)
@@ -2828,7 +2826,7 @@
 #endif
 
 	row -= W_WINROW(curwin);
-#ifdef FEAT_VERTSPLIT
+#ifdef FEAT_WINDOWS
 	col -= W_WINCOL(curwin);
 #endif
 
@@ -3089,7 +3087,6 @@
     {
 	if (fp->fr_layout == FR_LEAF)
 	    break;
-#ifdef FEAT_VERTSPLIT
 	if (fp->fr_layout == FR_ROW)
 	{
 	    for (fp = fp->fr_child; fp->fr_next != NULL; fp = fp->fr_next)
@@ -3099,7 +3096,6 @@
 		*colp -= fp->fr_width;
 	    }
 	}
-#endif
 	else    /* fr_layout == FR_COL */
 	{
 	    for (fp = fp->fr_child; fp->fr_next != NULL; fp = fp->fr_next)
@@ -3141,7 +3137,7 @@
      */
     if (row >= wp->w_height)	/* In (or below) status line */
 	return IN_STATUS_LINE;
-#ifdef FEAT_VERTSPLIT
+#ifdef FEAT_WINDOWS
     if (col >= wp->w_width)	/* In vertical separator line */
 	return IN_SEP_LINE;
 #endif