Certificate formatting and retrieval

This change introduces the implementation of the SSLConnection methods
getpeercert and cipher. The following has been added:

    * dtls.util:      utility elements shared by other modules in this package
    * dtls.x509:      a module for X509-certificate-related functionality,
                      including formatting a certificate into a Python
                      dictionary as prescribed by the Python standard
                      library's ssl module; functionality for testing with
                      PEM-encoded certificates in the file system is included
    * yahoo-cert.pem: the current certificate of www.yahoo.com: this is a good
                      testing certificate, since it contains the subject
                      alternate name extension

Other notable changes:

    * sslconnection:  private attributes are now preceded by "_"
    * openssl:        null-ness in opaque FuncParam-derived return values is
                      now properly detected and an exception is raised as
                      expected

dtls/test/certs/yahoo-cert.pem

@@ -0,0 +1,29 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

dtls/test/echo_seq.py

@@ -47,7 +47,7 @@ def main():
     print "Accepting..."
     conn = scn.accept()
     sck.settimeout(5)
-    conn.rsock.settimeout(5)
+    conn.get_socket(True).settimeout(5)
 
     cnt = 0
     while True:

dtls/test/rl.py

@@ -8,7 +8,9 @@ the IPython shell.
 
 import dtls
 import dtls.err
+import dtls.util
 import dtls.sslconnection
+import dtls.x509
 import dtls.openssl
 import dtls.demux
 import dtls.demux.router
@@ -16,11 +18,14 @@ import dtls.demux.router
 def main():
     reload(dtls)
     reload(dtls.err)
+    reload(dtls.util)
     reload(dtls.sslconnection)
+    reload(dtls.x509)
     reload(dtls.openssl)
     reload(dtls.demux)
     reload(dtls.demux.router)
     reload(dtls.sslconnection)
+    reload(dtls.x509)
 
 if __name__ == "__main__":
     main()