Fixes #3437 : the commit has been lost in the 2.3->2.4 merge, adding it back
Fixes #3495 - Add persistant classes to prevent rug or zypper to be too often used
Refs #3495 - Add expressions to definition of classes, reindent, use of curled braced instead of parenthesis and move body classes added into library.st
Refs #3495 - Add better descriptions and constraints to interval of time for check of packages installation
Refs #3495 - Update changelog
Merge pull request #97 from nperron/ust_3494/dev/3495_add_persistant_classes_to_prevent_use_of_pkgmgr

Fixes #3495 - Add persistant classes to prevent rug or zypper to be too often used
Merge branch 'branches/rudder/2.3' into branches/rudder/2.4
Merge rpmPackageInstallation/4.0/ from branch  2.3 to 2.4
Merge branch 'branches/rudder/2.4' into branches/rudder/2.5