Fix behavior of .INCLUDE within a macro or .REPEAT. In the original code

.INCLUDE was executed after expansion of the macro or .REPEAT - which was
wrong and caused all sorts of unexpected behavior. Related issues/PRs
are #231, #1473, #2159 and maybe others.

Note: After this change error messages for nested macro/.include statements
may be wrong. This is an unrelated bug that was always there and got exposed
by this fix. The bug needs to be addressed in a separate PR.

src/ca65/istack.c

@@ -156,3 +156,29 @@ void CheckInputStack (void)
         Error ("Open %s", IStack->Desc);
     }
 }
+
+
+
+InputStack RetrieveInputStack (void)
+/* Retrieve the current input stack. This will also clear it. Used when
+** including a file. The current input stack is stored together with the old
+** input file and restored when the file is closed.
+ */
+{
+    /* We do not touch the counter so input sources are counted across
+    ** includes.
+     */
+    InputStack S = IStack;
+    IStack = 0;
+    return S;
+}
+
+
+
+void RestoreInputStack (InputStack S)
+/* Restore an old input stack that was retrieved by RetrieveInputStack(). */
+{
+    CHECK (IStack == 0);
+    IStack = S;
+}
+