check method of private keys

[rick_dean]

Here is a patch to implement the RSA key checking functionality
of "openssl rsa -in somekey.pem -check -noout".

The openssl library (and applications) do not have the equivalent
functionality for DSA private keys, so attempting to check one produces
a TypeError exception.

Automated unit test cases are included, but I don't actually
have an inconsistent RSA key to test with, so the
failure explanation is not as detailed as the openssl app.

[rick_dean (rick-fdd)]

This patch add support for "openssl rsa -noout -modulus" and
"openssl dsa -noout -modulus". The patch applies on to of the
"-check" patch.

X509 seem to use "get_" in it's method names, but
PKey does not (see type()). This patch continues that
convention, but I'm open to change.

This patch duplicates the _runopenssl() function
definition in it's test case, but there is clearly
a better solution, although it would be
harder to merge.

[Jean-Paul Calderone (exarkun)]

The modulus patch confuses me a bit. It seems to be a faithful reimplementation of "openssl rsa -modulus" and "openssl dsa -modulus", but *those* options make little sense to me. Or rather, the RSA version makes sense, since RSA keys have something that can be referred to as a "modulus" with little confusion. Why you would make up the name "modulus" for the "public key components" of a DSA key is beyond me, though.

A use case would probably help clarify things. Meanwhile, I'll apply the `check` patch and resolve this ticket and push the `modulus` part to a branch so it can be dealt with easily when someone understands it. :)

[Jean-Paul Calderone (exarkun)]

PKey.check added. lp:~exarkun/pyopenssl/pkey-modulus has the modulus changes.