[Finder] Fix unexpected duplicate sub path related AppendIterator issue
[Finder] Fix iteration fails with non-rewindable streams
merged branch alquerci/ticket-3585-7834 (PR #8120)

This PR was squashed before being merged into the 2.1 branch (closes

Discussion
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[Finder] Fix iteration fails with non-rewindable streams

<table>
  <tr>
    <th>Q</th><th>A</th>
  </tr>
  <tr>
    <td>Bug fix?</td><td>yes</td>
  </tr>
  <tr>
    <td>New feature?</td><td>no</td>
  </tr>
  <tr>
    <td>BC breaks?</td><td>no</td>
  </tr>
  <tr>
    <td>Deprecations?</td><td>no</td>
  </tr>
  <tr>
    <td>Tests pass?</td><td>yes</td>
  </tr>
  <tr>
    <td>Fixed tickets</td><td>#3585, #7834</td>
  </tr>
  <tr>
    <td>License?</td><td>MIT</td>
  </tr>
</table>

- [x] Add a good detection of non seekable stream
- [x] Add some unit tests

But the iteration under ftp stream still not work properly. Edit: need
tests for that.

Commits
-------

169c0b9 [Finder] Fix iteration fails with non-rewindable streams
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