bug#16133: 24.3; copy-file fails on chmod when copying to FAT filesystem

[Glenn Morris]

I think you are right that it is a problem.
I think the problem was in documenting copy-file to always copy
permissions in the first place. But I imagine it is far too late to
change that. Not sure what the right thing to do is here...

Someone may be relying on the fact that copy-file copies permissions,
and want it it throw an error if it fails:

http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8306

Others, like you, may not care.

Since copy-file has only relatively recently starting giving an error,
maybe the least bad thing would be for it to give a message instead of
an error?

I don't know how we tidy this up for the future though.
Add yet another optional argument "error-if-permissions-fail"? Yuck.