patch 8.0.0806: tests may try to create XfakeHOME twice

Problem:    Tests may try to create XfakeHOME twice.
Solution:   Avoid loading setup.vim twice.
diff --git a/src/testdir/setup.vim b/src/testdir/setup.vim
index 6299852..31b133f 100644
--- a/src/testdir/setup.vim
+++ b/src/testdir/setup.vim
@@ -1,5 +1,13 @@
 " Common preparations for running tests.
 
+" Only load this once.
+if 1
+  if exists('s:did_load')
+    finish
+  endif
+  let s:did_load = 1
+endif
+
 " Make sure 'runtimepath' and 'packpath' does not include $HOME.
 set rtp=$VIM/vimfiles,$VIMRUNTIME,$VIM/vimfiles/after
 if has('packages')
diff --git a/src/version.c b/src/version.c
index ed7880c..cde101a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    806,
+/**/
     805,
 /**/
     804,