[SPARK-7137] [ML] Update SchemaUtils checkInputColumn to print more info if needed

Author: Joshi <rekhajoshm@gmail.com>
Author: Rekha Joshi <rekhajoshm@gmail.com>

Closes #5992 from rekhajoshm/fix/SPARK-7137 and squashes the following commits:

8c42b57 [Joshi] update checkInputColumn to print more info if needed
33ddd2e [Joshi] update checkInputColumn to print more info if needed
acf3e17 [Joshi] update checkInputColumn to print more info if needed
8993c0e [Joshi] SPARK-7137: Add checkInputColumn back to Params and print more info
e3677c9 [Rekha Joshi] Merge pull request #1 from apache/master

mllib/src/main/scala/org/apache/spark/ml/util/SchemaUtils.scala

@@ -32,10 +32,15 @@ private[spark] object SchemaUtils {
    * @param colName  column name
    * @param dataType  required column data type
    */
-  def checkColumnType(schema: StructType, colName: String, dataType: DataType): Unit = {
+  def checkColumnType(
+      schema: StructType,
+      colName: String,
+      dataType: DataType,
+      msg: String = ""): Unit = {
     val actualDataType = schema(colName).dataType
+    val message = if (msg != null && msg.trim.length > 0) " " + msg else ""
     require(actualDataType.equals(dataType),
-      s"Column $colName must be of type $dataType but was actually $actualDataType.")
+      s"Column $colName must be of type $dataType but was actually $actualDataType.$message")
   }
 
   /**