Set User source file to stdio

It was previously startup.m2.in, even though it's actually defined in
last.m2.  But stdio makes sense since that's where the user will
actually define the package's symbols.

Author: d-torrance

M2/Macaulay2/m2/last.m2

@@ -37,6 +37,7 @@ addStartFunction(
 		   DebuggingMode  => true);
 	       User.PackageIsLoaded = true;
 	       User#"source directory" = "";
+	       User#"source file" = "stdio";
 	       path = prepend("./",path); -- now we search also the user's current directory, since our files have already been loaded
 	       path = unique apply( path, minimizeFilename);	    -- beautify
 	       allowLocalCreation User#"private dictionary";