Conform foreach tparam to majority naming convention

'U' is the common choice for the foreach function result tparam.

This command summarises the naming diversity before and after this change.

$ fgrep -r 'def foreach[' *|cut -f2 -d:|cut -f1 -d'('|tr -s ' '|sed 's/override //g'|sort|uniq -c|sort -nr

Before,

     80  def foreach[U]
      6  def foreach[C]
      6  def foreach[B]
      4  final def foreach[U]
      3  def foreach[S]
      2  inline final def foreach[U]
      2  def foreach[A]
      1  inline final def foreach[specialized
      1  final def foreach[B]
      1  * def foreach[U]
      1  def foreach[Q]
      1  def foreach[D]
      1  def foreach[A,B,U]

After,

     98  def foreach[U]
      5  final def foreach[U]
      2  inline final def foreach[U]
      1  inline final def foreach[specialized
      1  * def foreach[U]
      1  def foreach[A,B,U]

(@ symbols removed.)

1 files changed, 1 insertions, 1 deletions

diff --git a/src/library/scala/collection/BitSetLike.scala b/src/library/scala/collection/BitSetLike.scala
index 8a8af79151..29369447d1 100644
--- a/src/library/scala/collection/BitSetLike.scala
+++ b/src/library/scala/collection/BitSetLike.scala
@@ -115,7 +115,7 @@ trait BitSetLike[+This <: BitSetLike[This] with SortedSet[Int]] extends SortedSe
       else Iterator.empty.next()
   }
 
-  override def foreach[B](f: Int => B) {
+  override def foreach[U](f: Int => U) {
     /* NOTE: while loops are significantly faster as of 2.11 and
        one major use case of bitsets is performance. Also, there
        is nothing to do when all bits are clear, so use that as