move "been here before" path concept into libardour, and use it appropriately at startup

gtk2_ardour/startup.cc

@@ -115,13 +115,23 @@ ArdourStartup::~ArdourStartup ()
 bool
 ArdourStartup::required ()
 {
-	return !Glib::file_test (been_here_before_path(), Glib::FILE_TEST_EXISTS);
-}
+	/* look for a "been here before" file for this version or earlier
+	 * versions
+	 */
 
-std::string
-ArdourStartup::been_here_before_path ()
-{
-	return Glib::build_filename (user_config_directory (), ".a" PROGRAM_VERSION);
+	const int current_version = atoi (PROGRAM_VERSION);
+	
+	for (int v = current_version; v != 0; --v) {
+		if (Glib::file_test (ARDOUR::been_here_before_path (v), Glib::FILE_TEST_EXISTS)) {
+			if (v != current_version) {
+				/* older version exists, create the current one */
+				ofstream fout (been_here_before_path (current_version).c_str());
+			}
+			return false;
+		}
+	}
+
+	return true;
 }
 
 void

gtk2_ardour/startup.h

@@ -60,8 +60,6 @@ class ArdourStartup : public Gtk::Assistant {
 	bool config_modified;
 	bool new_user;
 
-        static std::string been_here_before_path ();
-
 	void on_apply ();
 	void on_cancel ();
 	bool on_delete_event (GdkEventAny*);

libs/ardour/ardour/filesystem_paths.h

@@ -45,6 +45,14 @@ namespace ARDOUR {
 	 */
 	LIBARDOUR_API std::string user_cache_directory ();
 
+	/**
+	 * @return the path used to store a persistent indication
+	 * that the given version of the program has been used before.
+	 * 
+	 * @param version is the version to check for. If unspecified, 
+	 * it defaults to the current (build-time) version of the program.
+	 */
+	LIBARDOUR_API std::string been_here_before_path (int version = -1);
 
 	/**
 	 * @return the path to the directory that contains the system wide ardour

libs/ardour/filesystem_paths.cc

@@ -272,4 +272,15 @@ ardour_data_search_path ()
 	return search_path;
 }
 
+string
+been_here_before_path (int version)
+{
+	if (version < 0) {
+		version = atoi (PROGRAM_VERSION);
+	}
+
+	return Glib::build_filename (user_config_directory (version), string (".a") + to_string (version, std::dec));
+}
+
+
 } // namespace ARDOUR