Fix rs_file_copy_cb, which needs to know the position at which to copy.  Show fd# if copy fails.
Fix rs_file_copy_cb, which needs to know the position at which to
copy.  Show fd# if copy fails.

binondord/librsync,agrandville/librsync,Salamek/librsync,binondord/librsync,potatogim/librsync,dbaarda/librsync,VictorDenisov/librsync,sourcefrog/librsync,VictorDenisov/librsync,yrgoldteeth/librsync,Salamek/librsync,binondord/librsync,yrgoldteeth/librsync,pauloppenheim-liveloop/librsync,sourcefrog/librsync,pauloppenheim-liveloop/librsync-winbuild,dbaarda/librsync,pauloppenheim-liveloop/librsync,VictorDenisov/librsync,librsync/librsync,Salamek/librsync,librsync/librsync,pauloppenheim-liveloop/librsync-winbuild,librsync/librsync,pauloppenheim-liveloop/librsync,dbaarda/librsync,VictorDenisov/librsync,potatogim/librsync,potatogim/librsync,sourcefrog/librsync,agrandville/librsync,yrgoldteeth/librsync,dbaarda/librsync,librsync/librsync,agrandville/librsync,pauloppenheim-liveloop/librsync-winbuild,yrgoldteeth/librsync,sourcefrog/librsync