Identification and sensitivity fixes

These commits fixes issues related to fabiac forum requests and subsequent discussions with Johannes.

http://www.dynare.org/phpBB3/viewtopic.php?f=1&t=4355&p=10665&hilit=sensitivity#p10665
http://www.dynare.org/phpBB3/viewtopic.php?f=1&t=4402&p=10771&hilit=identification&sid=64c6f9d987a2641e79dd5722137eb483#p10771