Renew sliver error is not very clear

[nriga@bbn.com]

I was debugging something and ended up trying to renew a sliver for 20 days, the error I got was:

Failed to renew sliver urn:publicid:IDN+ch.geni.net:SampleClass+slice+oftuttest on unspecified_AM_URN (https://bbn-hn.exogeni.net:11443/orca/xmlrpc) (got result 'None'). Error from Aggregate: code 1: Requested new end date is after slice expiration or exceeds system default.

I am guessing that "exceeds system default" actually means "exceeds AM's maximum". It would be nice if the error was a bit more descriptive of the actual error and maybe return what is the AM maximum so that the experimenter does not repeatedly try to hit a date within the allowed timeframe.

And since I am creating a ticket it would be helpful if the two cases (>slice_expiration and >AM max) have separate errors to help the user understand where the error is and how to fix it.