Internals of OpenSSL::PKCS7 should be kept within ossl_pkcs7.c.

Add a new ossl_pkcs7_new() function for duplicating and wrapping an
OpenSSL PKCS7 object in OpenSSL::PKCS7. This follows the convention
used by other ossl_*_new() functions.

https://github.com/ruby/openssl/commit/b5f79f771e

A follow-up to commit https://github.com/ruby/openssl/commit/27e11f2d1dcd and https://github.com/ruby/openssl/commit/07eceb7f6326. The PKCS7 object
must be freed before raising an exception.

https://github.com/ruby/openssl/commit/172eee4665

Require that users explicitly specify the desired algorithm. In my
opinion, we are not in a position to specify the default cipher.

When OpenSSL::PKCS7.encrypt is given only two arguments, it uses
"RC2-40-CBC" as the symmetric cipher algorithm. 40-bit RC2 is a US
export-grade cipher and considered insecure.

Although this is technically a breaking change, the impact should be
minimal. Even when OpenSSL is compiled with RC2 support and the macro
OPENSSL_NO_RC2 is not defined, it will not actually work on modern
systems because RC2 is part of the legacy provider.

https://github.com/ruby/openssl/commit/439f456bfa

Update the references to the file "LICENCE" with "COPYING".

The file LICENCE doesn't exist in ruby/ruby nor ruby/openssl. This has
been always the case since OpenSSL for Ruby 2 was merged to the ruby
tree as a standard library in 2003.

In OpenSSL for Ruby 2's CVS repository[1], the LICENCE file contained
an old version of the Ruby License, identical to the COPYING file that
was in Ruby's tree at that time (r4128[2]).

[1] http://cvs.savannah.gnu.org/viewvc/rubypki/ossl2/LICENCE?revision=1.1.1.1&view=markup
[2] https://github.com/ruby/ruby/blob/231247c010acba191b78ed2d1310c935e63ad919/COPYING

https://github.com/ruby/openssl/commit/5bccf07d04

https://github.com/ruby/openssl/commit/71cd1e3f5c

[pkuzco: expanded the fix for other content types]
[ky: adjusted formatting and the exception type]

https://github.com/ruby/openssl/commit/07eceb7f63

Co-authored-by: pkuzco <b.naamneh@gmail.com>
Co-authored-by: Kazuki Yamaguchi <k@rhe.jp>

Fixes [Bug #19974]

[pkuzco: expanded the fix for other content types]
[ky: adjusted formatting and the exception type]

https://github.com/ruby/openssl/commit/27e11f2d1d

Co-authored-by: pkuzco <b.naamneh@gmail.com>
Co-authored-by: Kazuki Yamaguchi <k@rhe.jp>

The vast majority have no reference so it's just a matter of setting the flags.

For the couple exception, they have very little references so it's
easy.

https://github.com/ruby/openssl/commit/2c7c6de69e

Methods that take both PEM-encoding and DER-encoding have not been
consistent in the order in which encoding to attempt to parse.

A DER-encoding may contain a valid PEM block ("\n-----BEGIN ..-----" to
"-----END ...-----") embedded within it. Also, the PEM-encoding parser
allows arbitrary data around the PEM block and silently skips it. As a
result, attempting to parse data in DER-encoding as PEM-encoding first
can incorrectly finds the embedded PEM block instead.

This commit ensures that DER encoding will always be attempted before
PEM encoding. OpenSSL::X509::Certificate is one of the updated classes.
With this, the following will always be true:

    # obj is an OpenSSL::X509::Certificate
    obj == OpenSSL::X509::Certificate.new(obj.to_der)
    obj == OpenSSL::X509::Certificate.new(obj.to_pem)

https://github.com/ruby/openssl/commit/b280eb1fd0

ASN1_dup() will not copy the 'pkey' field of a PKCS7_SIGNER_INFO object
by design; it is a temporary field kept until the PKCS7 structure is
finalized. Let's bump reference counter of the pkey in the original
object and use it in the new object, too.

This commit also removes PKCS7#add_signer's routine to add the
content-type attribute as a signed attribute automatically. This
behavior was not documented or tested. This change should not break any
working user code since the method was completely useless without the
change above.

https://github.com/ruby/openssl/commit/20ca7a27a8