Make initial overwrites more user friendly

[ingydotnet]

When a user sets up ... on existing configured machine, it will backup and
overwrite their files.

If we only used the symlink method, then we could detect this and tell them
what we are doing and DTRTs.

Maybe make method required and then heavily suggest using symlink.

[wwalker]

Ingy.. great product! Thank you!

I just found today that my .bashrc.local had become unlinked from the source file in .../src/..... I have no idea how, nor do I know how many times in the past I've lost edits because of this.

I use the hard link method. I really like the hard link method.

However, using either hard or sym link method, an ill behaved app or editor can remove the file in the home dir and replace it with a local file.

So, it seems we should detect "if the target file is not a link to the source file". This could be done every time in do_backup.

I'll endeavor to create a patch for this. My perl is rusty, but....