ensure that the methods-package C code looks for its functions in its namespace and not on the search path

git-svn-id: https://svn.r-project.org/R/trunk@63624 00db46b3-68df-0310-9c12-caf00c1e9a41
check for unexpected top-level files

git-svn-id: https://svn.r-project.org/R/trunk@63626 00db46b3-68df-0310-9c12-caf00c1e9a41