crypto: fix to check ext method for shared lib

In the case of using openssl with shared library,
reinterpret_cast<X509V3_EXT_I2V>(i2v_GENERAL_NAMES)) refers plt
pointer so that SafeX509ExtPrint returns false.
Fix it to check it with method of NID_subject_alt_name

This patch originally was created by Fedor Indutny
and Ben Noordhuis

Fixes: https://github.com/iojs/io.js/issues/617
PR-URL: https://github.com/iojs/io.js/pull/800



Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Fedor Indutny <fedor@indutny.com>