Added validation check on mid in fusesma.R and fuserouting.R

It is important to make sure mid is an integer (it could be entered as a real number when RHydro uses hydromad functionalities) 

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/r-hydro@177 edb9625f-4e0d-4859-8d74-9fd3b1da38cb