merge SVN commit 1102607 by winterz:

some backend resources (like Kolab) don't necessarily provide a revision
number on their incidences. So in addition to check for revision number
changes, also check for last-modified date changes to detect if
an incidence has been edited since we last showed it in the korgac dialog.
kolab/issue4203

svn path=/tags/kdepim/enterprise35.0.20100312.1102367/kdepim/; revision=1102608