Updating user-startup fails

[gareth-smyth]

When an installer running under 68k Amiga OS tries to update an existing user-startup the temporary file is created, but fails to open so the installer quits.

I think it is an issue with the mode, i'll create a pull request for a fix.

[gareth-smyth]

This is the file i'm using to test

(startup "MyTest"
	(prompt "hello")
	(command "Run My Test")
	(help "some help")
)