Ignore warning on fopen
bug #11854 [FileSystem] Fix Throw Exception on copying from an unreadable file (Jérémy Derussé)

This PR was merged into the 2.6-dev branch.

Discussion
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[FileSystem] Fix Throw Exception on copying from an unreadable file

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        | NA

Two commits on `Filesystem::copy`  was merged on diffrentes branches c056a9c426af43920e543eaedc66fe919f0ae838 and cd5da9b3c879eac2665722cd5a4f7a2c726392e1 but on the merge operation a `@fopen` was transformed to `fopen` . Thas why, actualy, travis is down on master branch (https://travis-ci.org/symfony/symfony/jobs/34427199#L434)

Commits
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b30317e Ignore warning on fopen