revising coalescent simulator, heterochron samples

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/colgem@84 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
git-svn-id: svn://svn.r-forge.r-project.org/svnroot/colgem@85 edb9625f-4e0d-4859-8d74-9fd3b1da38cb