Bug#436752: Improve error message for altered initramfs

[sebastian.leske@sleske.name]

Package: initramfs-tools
Version: 0.88
Severity: minor

If the initramfs has been altered by a tool different from
update-initramfs, then update-initramfs will refuse to update it,
complaining:

"${initramfs} has been altered. Cannot update."

I found this message to be a bit confusing. It wasn't clear to my what
"has been altered" means, and what I can do about the message. Therefore
I propose a new wording for the message:

"${initramfs} has been altered since last run of
update-initramfs; not updating. Use option -t to override."

This explains just why update-initramfs is bailing, and tells users what
to do if they still want to go ahead.