undo the previous changes to intra_copy, it only works on files
undo the previous changes to intra_copy, it only works on files

 * can_intra_copy() will return False if the path to be copied is a
   directory, because GDrive does not support intra_copy for
   directories.  For the time being there's no need to made it do
   extra work if the metadata object being returned is always a file.
   Add a couple of comments to make this apparent to future us.

rdhyee/waterbutler,felliott/waterbutler,TomBaxter/waterbutler,RCOSDP/waterbutler,CenterForOpenScience/waterbutler