Bugfix: new DPI-controlled UI size code was setting 'view2d re-init'

flag on ED_area_initialize(). This however was causing 2 problems;
- the view state got reset (popping window view back)
- the view2d operator polls failed (sliders didnt work)

This re-init was only needed for the headers though, limiting it
to these types of regions solves it.

source/blender/editors/screen/area.c

@@ -967,7 +967,8 @@ void ED_area_initialize(wmWindowManager *wm, wmWindow *win, ScrArea *sa)
 			uiFreeBlocks(NULL, &ar->uiblocks);	
 		}
 		
-		/* rechecks all 2d matrices */
+		/* rechecks 2d matrix for header on dpi changing, do not do for other regions, it resets view && blocks view2d operator polls (ton) */
+		if(ar->regiontype==RGN_TYPE_HEADER)
 			ar->v2d.flag &= ~V2D_IS_INITIALISED;
 	}
 }

source/blender/editors/space_api/spacetypes.c

@@ -70,6 +70,9 @@ void ED_spacetypes_init(void)
 	const ListBase *spacetypes;
 	SpaceType *type;
 
+	/* UI_UNIT_X is now a variable, is used in some spacetype inits? */
+	U.widget_unit= 20;
+	
 	/* create space types */
 	ED_spacetype_outliner();
 	ED_spacetype_time();