add properties to getPeerCertificate to support foaf+ssl

[niclashoyer]

To use the node TLS interface for an foaf+ssl application we need some more information from the peer certificate that getPeerCertificate returns, especially

• subject alt name
• exponent
• modulus

There is already a patch submitted by Nathan Rixham in 2010, but he didn't sign the CLA yet [1]. As suggested by pquerna maybe there is a better solution for this [2].

[1] http://groups.google.com/group/nodejs/browse_thread/thread/1d42da4cb2e51536
[2] #1286