Use the new interface to RSA_generate_key if available

Some libssls, namely the one you can get precompiled for
Android, comes without any deprecated interfaces, and
thhose include RSA_generate_key; this stops the
module from working.

This commit makes the module use the new interface if
on a recent version of libssl.

For reference, I filed a similar patch against Net::SSLeay last month: https://rt.cpan.org/Public/Bug/Display.html?id=96820

...Honestly, this is really just for Android -- I doubt that any major distro is going to drop the deprecated interfaces any time soon. So if you'd like to minimize any chances of this causing problems, you could replace the

#if OPENSSL_VERSION_NUMBER >= 0x00908000L

with a

#ifdef __ANDROID__