Tramp saving backup file to read-only directory

[Jeff Costlow]

This has happened a couple times now.  Again, it's on cygwin emacs 21.
I happen to be opening a file using tramp-method "scp" on a remote RHEL
3 linux machine.

Open a file in a remote read-only directory.  I used /usr/include
pthread.h.  When it comes time for emacs to save the backup file, tramp
attempts to save the remote file in that directory.  It will fail, but
it will keep trying until emacs crashes.
I can't turn on tramp-verbose for this one because once it attempts to
write the backup file, nothing can stop it until emacs crashes.