Add abm12

git-svn-id: https://svnsrv.desy.de/basic/h1fitter/trunk@1556 b2a8d302-ca0a-427a-b7b9-081adbce06bc
Add symmetric Hessian support

git-svn-id: https://svnsrv.desy.de/basic/h1fitter/trunk@1557 b2a8d302-ca0a-427a-b7b9-081adbce06bc