Support duplicate file paths in tar archives

Duplicate path entries are made possible within tar archives, as per
feature request described in #849.

RELNOTES: Duplicate path entry support within tar archives

pkg/private/tar/tar_writer.py

@@ -125,14 +125,10 @@ def _addfile(self, info, fileobj=None):
       # Enforce the ending / for directories so we correctly deduplicate.
       if not info.name.endswith('/'):
         info.name += '/'
-    if not self._have_added(info.name):
-      self.tar.addfile(info, fileobj)
-      self.members.add(info.name)
-      if info.type == tarfile.DIRTYPE:
-        self.directories.add(info.name)
-    elif info.type != tarfile.DIRTYPE:
-      print('Duplicate file in archive: %s, '
-            'picking first occurrence' % info.name)
+    self.tar.addfile(info, fileobj)
+    self.members.add(info.name)
+    if info.type == tarfile.DIRTYPE:
+      self.directories.add(info.name)
 
   def add_directory_path(self,
                          path,
@@ -154,7 +150,7 @@ def add_directory_path(self,
       mode: unix permission mode of the file, default: 0755.
     """
     assert path[-1] == '/'
-    if not path or self._have_added(path):
+    if not path:
       return
     if _DEBUG_VERBOSITY > 1:
       print('DEBUG: adding directory', path)