Moved single firm handling out of lmAMM.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/eventstudies@301 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added test cases for testing eventstudy interfaces to various models.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/eventstudies@302 edb9625f-4e0d-4859-8d74-9fd3b1da38cb