add ddfKmeans method in ddf-R
through a bug in R func head()
change dataFrame to as.data
update
update KMeans and as.data.frame
deleted unused files
Merge pull request #31 from ddf-project/nhan-add-test-all-for-R-CMD-check

Now we can R CMD check package when standing at DDF/R directory
add end line
Merge pull request #30 from ljzzju/fixHeadBug

Fix head bug