delegation: add support for GridSite

This patch adds support for GridSite delegation v2.0.0.  The endpoint is run as
part of the SRM service and has the path /srm/delegation and allows a user to
delegate a credential, discover the remaining lifetime of any delegated credential
and destroy delegated credentials.  Those credentials delegated via SRM and httpg
have the delegated ID of 'gsi'.  Using this, a client may delete credentials
delegated via SRM operations.

Also included is a delegation client that allows scripted and console-based
interaction with GridSite endpoints.

Target: master
Requires-notes: true
Requires-book: true

grid-site delegation.  The end-point is the
same as the SRM endpoint, so any SRM client can discover the end-point
trivially.