MyProxy JGlobus 2.0 fixes from CILogon CVS

MyProxy JGlobus 2.0 fixes from CILogon CVS:
- use org.bouncycastle.util.encoders.Base64 instead of org.globus.util.Base64
- support list of MyProxy server hostnames/ports
- force GSS confidentiality
- handle multiple authz challenge options
- remove very old deprecated API