As we already discussed... when using save a copy it would be nice if the copy
would default to have the same permissions as the original file (if it exists).

This is useful for instance if you are working on the local copy of a script and
then want to save the working copy on a remote machine, without having to ssh to
the machine and mark the script as executable each time.

The attached patch seems to work fine for me, but sure some review would be
appreciated. The patch only tries to preserve the r/w/x bits for the owner,
group and others. It doesn't preserve the SUID, sticky bit etc.