More robust DMatrix creation from a sparse matrix (#1606)

* [CORE] DMatrix from sparse w/ explicit #col #row; safer arg types

* [python-package] c-api change for _init_from_csr _init_from_csc

* fix spaces

* [R-package] adopt the new XGDMatrixCreateFromCSCEx interface

* [CORE] redirect old sparse creators to new ones

R-package/R/xgb.DMatrix.R

@@ -27,7 +27,7 @@ xgb.DMatrix <- function(data, info = list(), missing = NA, ...) {
                     PACKAGE = "xgboost")
     cnames <- colnames(data)
   } else if (class(data) == "dgCMatrix") {
-    handle <- .Call("XGDMatrixCreateFromCSC_R", data@p, data@i, data@x,
+    handle <- .Call("XGDMatrixCreateFromCSC_R", data@p, data@i, data@x, nrow(data),
                     PACKAGE = "xgboost")
     cnames <- colnames(data)
   } else {