Fix several instances of doubled words

One in an exception; the rest in docblocks.
Merge branch '2.1' into 2.2

* 2.1:
  Fix several instances of doubled words
  [Finder] Fix iteration fails with non-rewindable streams
  [Finder] Fix unexpected duplicate sub path related AppendIterator issue
  Added type of return value in VoterInterface.
  Fixed two bugs in HttpCache

Conflicts:
	src/Symfony/Component/Finder/Tests/FinderTest.php