merge SVN commits 1007994,1008004,1008005,1008129 by winterz:

Make life easier by using the separate class files for AssignmentVisitor
and ComparisonVisitor. Copied from trunk.

When an invitation incidence is being updated only, do not delete-then-add
the incidence to the calendar; instead, use and AssignmentVisitor to
simply assign the update. This is better because the user is not
prompted with a Resource Selector dialog with a simple assignment.

and when the user is not prompted they are not allowed to move
the incidence to a different calendar resource -- which can lead
to sorts of trouble.

kolab/issue3776

svn path=/tags/kdepim/enterprise35.0.20090731.1005176/kdepim/; revision=1008133