Timestamping verfication refs #44

Dedicated openssl call for TSA validation.

Remains problem of OCSP verification:
OCSP URL: http://ocsp.pre.swissdigicert.ch/sdcs-tss2
Response Verify Failure
2710938092:error:27069065:OCSP routines:OCSP_basic_verify:certificate
verify error:ocsp_vfy.c:126:Verify error:unable to get local issuer
certificate

OK on myfile.t7s with following details:
 Signed by    : subject= C=ch,O=Swisscom,OU=Digital Certificate
Service,CN=Swisscom TEST TSA 3
                issuer= C=ch,O=Swisscom,OU=Digital Certificate
Services,CN=Swisscom TEST TSS CA 2
                validity= notBefore=Jun  5 12:46:53 2012 GMT
notAfter=Jun  5 12:46:53 2015 GMT
 OCSP check   : unknown