patch 8.0.1162: shared script for tests cannot be included twice

Problem:    Shared script for tests cannot be included twice.
Solution:   Include it where needed, it will "finish" if loaded again.

src/testdir/test_alot.vim

@@ -1,8 +1,6 @@
 " A series of tests that can run in one Vim invocation.
 " This makes testing go faster, since Vim doesn't need to restart.
 
-source shared.vim
-
 set belloff=all
 source test_assign.vim
 source test_bufline.vim

src/testdir/test_bufline.vim

@@ -1,8 +1,6 @@
 " Tests for setbufline() and getbufline()
 
-if !exists('*GetVimCommand')
-  source shared.vim
-endif
+source shared.vim
 
 func Test_setbufline_getbufline()
   new

src/testdir/test_timers.vim

@@ -4,9 +4,7 @@ if !has('timers')
   finish
 endif
 
-if !exists('*WaitFor')
-  source shared.vim
-endif
+source shared.vim
 
 func MyHandler(timer)
   let g:val += 1

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1162,
 /**/
     1161,
 /**/