[SPARK-6455] [docs] Correct some mistakes and typos

Correct some typos. Correct a mistake in lib/PageRank.scala. The first PageRank implementation uses standalone Graph interface, but the second uses Pregel interface. It may mislead the code viewers.

Author: Hangchen Yu <yuhc@gitcafe.com>

Closes #5128 from yuhc/master and squashes the following commits:

53e5432 [Hangchen Yu] Merge branch 'master' of https://github.com/yuhc/spark
67b77b5 [Hangchen Yu] [SPARK-6455] [docs] Correct some mistakes and typos
206f2dc [Hangchen Yu] Correct some mistakes and typos.

Author: Hangchen Yu

graphx/src/main/scala/org/apache/spark/graphx/GraphOps.scala

@@ -113,7 +113,7 @@ class GraphOps[VD: ClassTag, ED: ClassTag](graph: Graph[VD, ED]) extends Seriali
    * Collect the neighbor vertex attributes for each vertex.
    *
    * @note This function could be highly inefficient on power-law
-   * graphs where high degree vertices may force a large ammount of
+   * graphs where high degree vertices may force a large amount of
    * information to be collected to a single location.
    *
    * @param edgeDirection the direction along which to collect
@@ -187,7 +187,7 @@ class GraphOps[VD: ClassTag, ED: ClassTag](graph: Graph[VD, ED]) extends Seriali
 
   /**
    * Join the vertices with an RDD and then apply a function from the
-   * the vertex and RDD entry to a new vertex value.  The input table
+   * vertex and RDD entry to a new vertex value.  The input table
    * should contain at most one entry for each vertex.  If no entry is
    * provided the map function is skipped and the old value is used.
    *

graphx/src/main/scala/org/apache/spark/graphx/Pregel.scala

@@ -78,8 +78,8 @@ object Pregel extends Logging {
    *
    * @param graph the input graph.
    *
-   * @param initialMsg the message each vertex will receive at the on
-   * the first iteration
+   * @param initialMsg the message each vertex will receive at the first
+   * iteration
    *
    * @param maxIterations the maximum number of iterations to run for
    *

graphx/src/main/scala/org/apache/spark/graphx/lib/PageRank.scala

@@ -25,7 +25,7 @@ import org.apache.spark.graphx._
 /**
  * PageRank algorithm implementation. There are two implementations of PageRank implemented.
  *
- * The first implementation uses the [[Pregel]] interface and runs PageRank for a fixed number
+ * The first implementation uses the standalone [[Graph]] interface and runs PageRank for a fixed number
  * of iterations:
  * {{{
  * var PR = Array.fill(n)( 1.0 )
@@ -38,7 +38,7 @@ import org.apache.spark.graphx._
  * }
  * }}}
  *
- * The second implementation uses the standalone [[Graph]] interface and runs PageRank until
+ * The second implementation uses the [[Pregel]] interface and runs PageRank until
  * convergence:
  *
  * {{{