SPARK-1539: RDDPage.scala contains RddPage class

SPARK-1386 changed RDDPage to RddPage but didn't change the filename. I tried sbt/sbt publish-local. Inside the spark-core jar, the unit name is RDDPage.class and hence I got the following error:

~~~
[error] (run-main) java.lang.NoClassDefFoundError: org/apache/spark/ui/storage/RddPage
java.lang.NoClassDefFoundError: org/apache/spark/ui/storage/RddPage
	at org.apache.spark.ui.SparkUI.initialize(SparkUI.scala:59)
	at org.apache.spark.ui.SparkUI.<init>(SparkUI.scala:52)
	at org.apache.spark.ui.SparkUI.<init>(SparkUI.scala:42)
	at org.apache.spark.SparkContext.<init>(SparkContext.scala:215)
	at MovieLensALS$.main(MovieLensALS.scala:38)
	at MovieLensALS.main(MovieLensALS.scala)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
Caused by: java.lang.ClassNotFoundException: org.apache.spark.ui.storage.RddPage
	at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
	at org.apache.spark.ui.SparkUI.initialize(SparkUI.scala:59)
	at org.apache.spark.ui.SparkUI.<init>(SparkUI.scala:52)
	at org.apache.spark.ui.SparkUI.<init>(SparkUI.scala:42)
	at org.apache.spark.SparkContext.<init>(SparkContext.scala:215)
	at MovieLensALS$.main(MovieLensALS.scala:38)
	at MovieLensALS.main(MovieLensALS.scala)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
~~~

This can be fixed after renaming RddPage to RDDPage, or renaming RDDPage.scala to RddPage.scala. I chose the former since the name `RDD` is common in Spark code.