fix _script_factory name clash, how the heck is this supposed to work at all?

Originally committed to SVN as r915.

aegisub/auto4_auto3.cpp

@@ -1452,6 +1452,6 @@ continue_invalid_option:
 			}
 		}
 	};
-	Auto3ScriptFactory _script_factory;
+	Auto3ScriptFactory _auto3_script_factory;
 
 };

aegisub/auto4_lua.cpp

@@ -890,6 +890,6 @@ namespace Automation4 {
 			}
 		}
 	};
-	LuaScriptFactory _script_factory;
+	LuaScriptFactory _lua_script_factory;
 
 };

aegisub/auto4_ruby.cpp

@@ -484,7 +484,7 @@ namespace Automation4 {
 			}
 		}
 	};
-	RubyScriptFactory _script_factory;
+	RubyScriptFactory _ruby_script_factory;
 
 	RubyObjects::RubyObjects()
 	{