patch 8.0.1161: popup menu drawing problem when resizing terminal

Problem:    Popup menu drawing problem when resizing terminal.
Solution:   Redraw after resizing also when a popup menu is visible. (Ozaki
            Kiichi, closes #2110)
diff --git a/src/testdir/shared.vim b/src/testdir/shared.vim
index 691199a..be83732 100644
--- a/src/testdir/shared.vim
+++ b/src/testdir/shared.vim
@@ -1,5 +1,10 @@
 " Functions shared by several tests.
 
+" Only load this script once.
+if exists('*WaitFor')
+  finish
+endif
+
 " Get the name of the Python executable.
 " Also keeps it in s:python.
 func PythonProg()