bug fix in rcolgem.R: if there is only one deme, then line 1761 returns a vector that causes problems when subsequent code tries to slice a column. Cast with as.matrix() to enforce column access.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/colgem@120 edb9625f-4e0d-4859-8d74-9fd3b1da38cb