Added condition to check date-time class column inside events list.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/eventstudies@375 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Fixed example, one other small modification.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/eventstudies@376 edb9625f-4e0d-4859-8d74-9fd3b1da38cb