patch 8.0.0708: some tests are old style

Problem:    Some tests are old style.
Solution:   Change a few tests from old style to new style. (pschuh,
            closes #1813)

src/testdir/test_exec_while_if.vim

@@ -0,0 +1,53 @@
+" Test for :execute, :while and :if
+
+function Test_exec_while_if()
+  new
+
+  let i = 0
+  while i < 12
+    let i = i + 1
+    if has("ebcdic")
+      execute "normal o" . i . "\047"
+    else
+      execute "normal o" . i . "\033"
+    endif
+    if i % 2
+      normal Ax
+      if i == 9
+        break
+      endif
+      if i == 5
+        continue
+      else
+        let j = 9
+        while j > 0
+          if has("ebcdic")
+            execute "normal" j . "a" . j . "\x27"
+          else
+            execute "normal" j . "a" . j . "\x1b"
+          endif
+          let j = j - 1
+        endwhile
+      endif
+    endif
+    if i == 9
+      if has("ebcdic")
+        execute "normal Az\047"
+      else
+        execute "normal Az\033"
+      endif
+    endif
+  endwhile
+  unlet i j
+
+  call assert_equal(["",
+        \ "1x999999999888888887777777666666555554444333221",
+        \ "2",
+        \ "3x999999999888888887777777666666555554444333221",
+        \ "4",
+        \ "5x",
+        \ "6",
+        \ "7x999999999888888887777777666666555554444333221",
+        \ "8",
+        \ "9x"], getline(1, 10))
+endfunction