Implementing support for continuing server subscriptions handled by SubscriptionHandler in case a NOTIFY is responded with an error response. In such case the NOTIFY transaction will be terminated but the subscription will continue until expiration. Application using resip DUM remains responsible for trying to resend the failed NOTIFY.

Application using DUM can configure if this functionality is enabled or not and for which
 error response codes the subscription should continue.
fixed a crash in subscription server when receiving a subscribe with expires: 0
renamed feature to a better name: "additionalTransationTerminatingResponses"
added documentation explaining why this is useful and how to enable it
Merge pull request #9 from SIPfoundry/master

-Implementing support for continuing server subscriptions handled by 
SubscriptionHandler in case a NOTIFY is responded with an error 
response. In such case the NOTIFY transaction will be terminated 
but the subscription will continue until expiration. Application
using resip DUM remains responsible for trying to resend the 
failed NOTIFY.  Application using DUM can configure if this 
functionality is enabled or not and for which error response 
codes the subscription should continue.  See MasterProfile
additionalTransationTerminatingResponses API's.

-fixed a crash in subscription server when receiving a subscribe 
 with expires: 0