Minor change: turn an error log message into a debug log message

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Add a target_find() helper to retrieve a target by its name

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Print the iSNS attribute value to the debug output if it is ignored

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Add interval timer functions based on timerfd

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Refresh the iSNS registration to prevent its expiration

Section 6.2.6 of the iSNS RFC says as follow:

  http://tools.ietf.org/html/rfc4171#section-6.2.6

  "The registration SHALL be removed from the iSNS database if an iSNS
   Protocol message is not received from the iSNS client before the
   registration period has expired. [...] To prevent a registration
   from expiring, the iSNS client should send an iSNS Protocol message
   to the iSNS server at intervals shorter than the registration
   period."

When registering a target, target-isns now specifies a registration
period to the iSNS server. A timer is used to refresh the registration
before it expires. The registration period is set to 5 minutes.

This patch fixes issue #4.

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Upgrade version to 0.2

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>