Refresh agent.properties file

[thboileau]

suggested by Daz, cf http://restlet.tigris.org/ds/viewMessage.do?dsForumId=4447&dsMessageId=3077839

[jlouvel]

Moved to 2.2.2 milestone.

[jlouvel]

We need to "Either make getAgentName() not return null or update the agent.properties file. Now I'm always checking whether getAgentName() is returning null or not."