POSIX only specifies the -H, -L, and -P options for use with -R, and
the default is left to the implementation. Without -R, symlinks must
be followed.
Most implementations use -P as the default with -R, which makes sense
to me as default behavior (the source and destination trees are the same).
Since we use the same code for -R and without it, and we allow -H, -L,
and -P without -R, set the default based on the presence of -R. Without
it, use -L as before, as required by POSIX, and with it, use -P to match
the behavior of other implementations.
f4b9b966cf