https://github.com/rubygems/rubygems/commit/132a56569d

String#sum(0) sums the character bytes without a modulo.
Follow-up of #6476 based on comment from @nobu.

https://github.com/rubygems/rubygems/commit/97add0d1d7

TarReader#each previously implemented a partial version of seek.
This code moved to Entry#seek for use from TarReader#each.

Entry#close now returns nil instead of true, like IO#close.

Closing an Entry now seeks to the end of the Entry, seeking past
any remaining zero byte tar file padding and moving the io to the
correcty position to read the next file in the archive.

Uses seek for Entry#rewind and #pos=, fixing the tar->gzip->tar nested
rewind that would break previous to this change.

Add Entry.open that behaves more like File.open.

https://github.com/rubygems/rubygems/commit/f5149565d5

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

  https://github.com/rubygems/rubygems/commit/125415593ead9ab69a9f0bb5392c9d7ec61b1f51

This changes "test/rubygems/test_case.rb" to "test/rubygems/helper.rb",
and "test/rubygems/test_utilities.rb" to "test/rubygems/utilities.rb".

The two files are a helper for tests, not test files. However, a file
starting with "test_" prefix is handled as a test file directly loaded
by test-unit because Rakefile specifies:

```
t.test_files = FileList['test/**/test_*.rb']
```

Directly loading test/rubygems/test_utilities.rb caused "uninitialized
constant Gem::TestCase". This issue was fixed by
59c682097197fee4052b47e4b4ab86562f3eaa9b, but the fix caused a
"circular require" warning because test_utilities.rb and test_case.rb
are now requiring each other.

Anyway, adding "test_" prefix to a test helper file is confusing, so
this changeset reverts the fix and solve the issue by renaming them.

https://github.com/rubygems/rubygems/commit/6460e018df

https://github.com/rubygems/rubygems/commit/c77868a555