[SPARK-6291] [MLLIB] GLM toString & toDebugString

GLM toString prints out intercept, numFeatures.
For LogisticRegression and SVM model, toString also prints out numClasses, threshold.
GLM toDebugString prints out the whole weights, intercept.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #5038 from yanboliang/spark-6291 and squashes the following commits:

2f578b0 [Yanbo Liang] code format
78b33f2 [Yanbo Liang] fix typos
1e8a023 [Yanbo Liang] GLM toString & toDebugString

mllib/src/main/scala/org/apache/spark/mllib/classification/LogisticRegression.scala

@@ -163,6 +163,10 @@ class LogisticRegressionModel (
   }
 
   override protected def formatVersion: String = "1.0"
+
+  override def toString: String = {
+    s"${super.toString}, numClasses = ${numClasses}, threshold = ${threshold.get}"
+  }
 }
 
 object LogisticRegressionModel extends Loader[LogisticRegressionModel] {

mllib/src/main/scala/org/apache/spark/mllib/classification/SVM.scala

@@ -86,6 +86,10 @@ class SVMModel (
   }
 
   override protected def formatVersion: String = "1.0"
+
+  override def toString: String = {
+    s"${super.toString}, numClasses = 2, threshold = ${threshold.get}"
+  }
 }
 
 object SVMModel extends Loader[SVMModel] {

mllib/src/main/scala/org/apache/spark/mllib/regression/GeneralizedLinearAlgorithm.scala

@@ -76,7 +76,12 @@ abstract class GeneralizedLinearModel(val weights: Vector, val intercept: Double
     predictPoint(testData, weights, intercept)
   }
 
-  override def toString() = "(weights=%s, intercept=%s)".format(weights, intercept)
+  /**
+   * Print a summary of the model.
+   */
+  override def toString: String = {
+    s"${this.getClass.getName}: intercept = ${intercept}, numFeatures = ${weights.size}"
+  }
 }
 
 /**