Replace cBind by cbind (#3203)

* modify test_helper.R

* fix noLD

* update desc

* fix solaris test

* fix desc

* improve fix

* fix url

* change Matrix cBind to cbind

* fix

* fix error in demo

* fix examples

R-package/NAMESPACE

@@ -51,7 +51,6 @@ export(xgboost)
 import(methods)
 importClassesFrom(Matrix,dgCMatrix)
 importClassesFrom(Matrix,dgeMatrix)
-importFrom(Matrix,cBind)
 importFrom(Matrix,colSums)
 importFrom(Matrix,sparse.model.matrix)
 importFrom(Matrix,sparseMatrix)