`tar_writer.py`: address duplicate dir warning regression (#900)

* `tar_writer.py`: address duplicate dir warning regression

* `tar_writer.py`: comment dir dup check

* `tar_writer.py`: omit warning for duplicate dirs

pkg/private/tar/tar_writer.py

diff --git a/pkg/private/tar/tar_writer.py b/pkg/private/tar/tar_writer.py
index 4495e5c..6c0d926 100644
--- a/pkg/private/tar/tar_writer.py
+++ b/pkg/private/tar/tar_writer.py
@@ -130,9 +130,12 @@
       if not info.name.endswith('/'):
         info.name += '/'
     if not self.allow_dups_from_deps and self._have_added(info.name):
+      # Directories with different contents should get merged without warnings.
+      # If they have overlapping content, the warning will be on their duplicate *files* instead
+      if info.type != tarfile.DIRTYPE:
         print('Duplicate file in archive: %s, '
               'picking first occurrence' % info.name)
-        return
+      return
 
     self.tar.addfile(info, fileobj)
     self.members.add(info.name)