ignore environment and profile files

This pull request provides a fix for the problem I faced at https://github.com/ropensci/webservices/pull/56

Details: I set the working directory to `/tmp` in my `.Rprofile` -- that's why `XML::xmlTreeParse` cannot find `WebTechnologies.ctv`. Adding `--vanilla` option to the `Rscript` call in the `Makefile` would also help some other possible issues.

Please feel free to merge or close.