Add fileSnapshot and changedFiles function.

git-svn-id: https://svn.r-project.org/R/trunk@63888 00db46b3-68df-0310-9c12-caf00c1e9a41
Fix line endings

git-svn-id: https://svn.r-project.org/R/trunk@63889 00db46b3-68df-0310-9c12-caf00c1e9a41