Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0
Currently 'cp' defaults to not using reflinks, which can be
significantly slower on a system that supports file cloning. I expect
most users would prefer 'cp' to default to --reflink=auto for spped.
Although there are some special cases otherwise, on balance how about if
we change cp to default to --reflink=auto, and add an option
--reflink=no for users who prefer the current default?