(2.2) javatunnel: add certificate chain to subject

Failing XACML authentication through the gsidcap door.

The issue is that XACML, being both an auth and map plugin, requires the full certificate chain to be in the Subject.  The gsi tunnel was

The tunnel now extracts the chain from the GSSCredential object and places it in the public credentials set of the subject.

Testing:

Before the patch, the XACML plugin would fail because it had incomplete information and which it processed in a faulty manner.  The error

    [DCap-gsi-00-fndca4a-/DC=com/DC=DigiCert-Grid/O=Open Science
    Grid/OU=People/CN=Kenneth Herner 1385-133 Login AUTH xacml] mapping
    service
    https://gums.fnal.gov:8443/gums/services/GUMSXACMLAuthorizationServicePort
    returned localId LocalId[] for VomsExtensions[X509Subject='/fermilab',
    X509SubjectIssuer='null', fqan='null', primary=false, VO='null',
    VOMSSubject='null', VOMSSubjectIssuer='null']

After the patch, the dccp operation succeeds.

Target: 2.2
Patch: http://rb.dcache.org/r/6112/
Require-book: no
Require-notes: yes
Acked-by: Tigran
Committed: 43d81f7b167ddfeec311f6eb24283e1251e6d0b5

RELEASE NOTES:
Fixes a bug whereby a combination of gsidcap with a VOMS cert and XACML authentication/mapping failed to authorize the user.
Merge pull request #234 from alrossi/fix/2.2/gsi-tunnel-x509-chain

(2.2) javatunnel: add certificate chain to subject