Add test case for symbol coercion in C Babel blocks

The ORG-NEWS entry for version 9.1 suggests that this coercion was
always intended, though AFAICT there was no test case for it.

* testing/lisp/test-ob-C.el (ob-C/symbol-include): Check explicitly
that :includes <iostream> (with no double-quotes around <iostream>)
will be parsed correctly.
(ob-D/simple-program, ob-C/integer-var, ob-D/integer-var,
ob-C/two-integer-var, ob-D/two-integer-var, ob-C/string-var,
ob-D/string-var, ob-C/preprocessor): Adjust block indices.

* testing/examples/ob-C-test.org (Simple tests): Add input for the new
test.

testing/examples/ob-C-test.org

@@ -10,6 +10,12 @@
   return 0;
 #+end_src
 
+#+source: simple
+#+begin_src cpp :includes <iostream> :results silent
+  std::cout << 42;
+  return 0;
+#+end_src
+
 #+source: simple
 #+begin_src D :results silent
   writefln ("%s", 42);

testing/lisp/test-ob-C.el

@@ -32,60 +32,67 @@
 		      (org-babel-next-src-block 1)
 		      (should (= 42 (org-babel-execute-src-block))))))
 
+(ert-deftest ob-C/symbol-include ()
+  "Hello world program with unquoted :includes."
+  (if (executable-find org-babel-C++-compiler)
+      (org-test-at-id "fa6db330-e960-4ea2-ac67-94bb845b8577"
+		      (org-babel-next-src-block 2)
+		      (should (= 42 (org-babel-execute-src-block))))))
+
 (ert-deftest ob-D/simple-program ()
   "Hello world program."
   (if (executable-find org-babel-D-compiler)
       (org-test-at-id "fa6db330-e960-4ea2-ac67-94bb845b8577"
-		      (org-babel-next-src-block 2)
+		      (org-babel-next-src-block 3)
 		      (should (= 42 (org-babel-execute-src-block))))))
 
 (ert-deftest ob-C/integer-var ()
   "Test of an integer variable."
   (if (executable-find org-babel-C++-compiler)
       (org-test-at-id "fa6db330-e960-4ea2-ac67-94bb845b8577"
-		      (org-babel-next-src-block 3)
+		      (org-babel-next-src-block 4)
 		      (should (= 12 (org-babel-execute-src-block))))))
 
 (ert-deftest ob-D/integer-var ()
   "Test of an integer variable."
   (if (executable-find org-babel-D-compiler)
       (org-test-at-id "fa6db330-e960-4ea2-ac67-94bb845b8577"
-		      (org-babel-next-src-block 4)
+		      (org-babel-next-src-block 5)
 		      (should (= 12 (org-babel-execute-src-block))))))
 
 (ert-deftest ob-C/two-integer-var ()
   "Test of two input variables"
   (if (executable-find org-babel-C++-compiler)
       (org-test-at-id "fa6db330-e960-4ea2-ac67-94bb845b8577"
-		      (org-babel-next-src-block 5)
+		      (org-babel-next-src-block 6)
 		      (should (= 22 (org-babel-execute-src-block))))))
 
 (ert-deftest ob-D/two-integer-var ()
   "Test of two input variables"
   (if (executable-find org-babel-D-compiler)
       (org-test-at-id "fa6db330-e960-4ea2-ac67-94bb845b8577"
-		      (org-babel-next-src-block 6)
+		      (org-babel-next-src-block 7)
 		      (should (= 22 (org-babel-execute-src-block))))))
 
 (ert-deftest ob-C/string-var ()
   "Test of a string input variable"
   (if (executable-find org-babel-C++-compiler)
       (org-test-at-id "fa6db330-e960-4ea2-ac67-94bb845b8577"
-		      (org-babel-next-src-block 7)
+		      (org-babel-next-src-block 8)
 		      (should (equal "word 4" (org-babel-execute-src-block))))))
 
 (ert-deftest ob-D/string-var ()
   "Test of a string input variable"
   (if (executable-find org-babel-D-compiler)
       (org-test-at-id "fa6db330-e960-4ea2-ac67-94bb845b8577"
-		      (org-babel-next-src-block 8)
+		      (org-babel-next-src-block 9)
 		      (should (equal "word 4" (org-babel-execute-src-block))))))
 
 (ert-deftest ob-C/preprocessor ()
   "Test of a string variable"
   (if (executable-find org-babel-C++-compiler)
       (org-test-at-id "fa6db330-e960-4ea2-ac67-94bb845b8577"
-		      (org-babel-next-src-block 9)
+		      (org-babel-next-src-block 10)
 		      (should (= 42 (org-babel-execute-src-block))))))
 
 (ert-deftest ob-C/table ()