Don't break if there are no successful outcomes, return NULL instead. Can handle univariate series now. All tests passing.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/eventstudies@252 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Don't print no inference strategy warning for one series if inference was originally FALSE.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/eventstudies@253 edb9625f-4e0d-4859-8d74-9fd3b1da38cb