API to detect the bound version of OpenSSL

[bartonjs]

Since SafeEvpPKeyHandle exists to allow interop with OpenSSL, it would be good for callers to be able to determine if they are using the same library/version of OpenSSL that we are.

    public sealed partial class SafeEvpPKeyHandle
    {
        // The result of SSLeay() (OpenSSL 1.0.2) or OpenSSL_version() (OpenSSL 1.1.x)
        public static int OpenSslVersion { get; }
    }

Discussion points:

• The native API is Unix C-long, so 32-bit on 32-bit, 64-bit on 64-bit.
• So, int, uint, long, or ulong?
• The version number contains detail we can't expose via System.Version
• Callers are only expected to do ==

[stephentoub]

SafeEvpPKeyHandle

Seems like a strange place to put it. Could we put it on another type with OpenSSL in the name, that's not a SafeHandle, etc.? Even if it meant introducing a new type?

The version number contains detail we can't expose via System.Version

But they can be exposed in an int/long?

[vcsjones]

But they can be exposed in an int/long?

They cram a bunch of information in different bits. e.g.:

0x000906023 == 0.9.6b beta 3

[stephentoub]

They cram a bunch of information in different bits

I see. Thanks.

[terrajobst]

Looks good, but we should make the return type long.