Require removing prior version of Rcpp

[Katharina Gerstner]

Downloading the latest version of MoBspatial gives me the following error message:

install_github('MoBiodiv/MoBspatial')
Downloading GitHub repo MoBiodiv/MoBspatial@master
from URL https://api.github.com/repos/MoBiodiv/MoBspatial/zipball/master
Installing MoBspatial
Installing 1 package: Rcpp
package ‘Rcpp’ successfully unpacked and MD5 sums checked
Warning: cannot remove prior installation of package ‘Rcpp’
[...]
ERROR: dependency 'Rcpp' is not available for package 'MoBspatial'
[...]

I remember installing 'Rcpp' is not the easiest task. So what about skipping if not yet installed and creating a warning.