Quickbook: Parse templates using the version they were defined for.

Needs to store the version in the file object, since it's only known
after the file is read in, had to make files non-const. Put some checks
in to make sure this isn't abused but pretty messy.

[SVN r75260]

src/quickbook.cpp

@@ -130,7 +130,8 @@ namespace quickbook
             actions actor(filein_, xinclude_base_, buffer, ids);
             set_macros(actor);
 
-            actor.current_file = load(filein_); // Throws load_error
+            actor.current_file_tmp = load(filein_); // Throws load_error
+            actor.current_file = actor.current_file_tmp;
 
             parse_file(actor);