- make 'abc' class definition compatible with older versions of R
- remove unneeded duplication of 'gnsi' in some C codes
- oldest version of R against which package checked is 2.15.1


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/pomp@911 edb9625f-4e0d-4859-8d74-9fd3b1da38cb