[SQL] Fixed 2 comment typos in SQLConf

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #2172 from liancheng/sqlconf-typo and squashes the following commits:

115cc71 [Cheng Lian] Fixed 2 comment typos in SQLConf

sql/core/src/main/scala/org/apache/spark/sql/SQLConf.scala

@@ -92,7 +92,7 @@ trait SQLConf {
    * When set to true, Spark SQL will use the Scala compiler at runtime to generate custom bytecode
    * that evaluates expressions found in queries.  In general this custom code runs much faster
    * than interpreted evaluation, but there are significant start-up costs due to compilation.
-   * As a result codegen is only benificial when queries run for a long time, or when the same
+   * As a result codegen is only beneficial when queries run for a long time, or when the same
    * expressions are used multiple times.
    *
    * Defaults to false as this feature is currently experimental.
@@ -111,8 +111,9 @@ trait SQLConf {
 
   /**
    * The default size in bytes to assign to a logical operator's estimation statistics.  By default,
-   * it is set to a larger value than `autoConvertJoinSize`, hence any logical operator without a
-   * properly implemented estimation of this statistic will not be incorrectly broadcasted in joins.
+   * it is set to a larger value than `autoBroadcastJoinThreshold`, hence any logical operator
+   * without a properly implemented estimation of this statistic will not be incorrectly broadcasted
+   * in joins.
    */
   private[spark] def defaultSizeInBytes: Long =
     getConf(DEFAULT_SIZE_IN_BYTES, (autoBroadcastJoinThreshold + 1).toString).toLong