fixed Client implementation to return the right Response (closes #4475)
alternate fix where we had accessor for the BrowerKit request/response instances
made some small tweaks
merged branch fabpot/browserkit-client (PR #7835)

This PR was merged into the master branch.

Discussion
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fixed Client implementation to return the right Response (closes #4475)

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #4475
| License       | MIT
| Doc PR        | symfony/symfony-docs#2549

This PR addresses #4475 by trying to minimize the BC break impact.

Commits
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31cefc6 made some small tweaks
84ca34b alternate fix where we had accessor for the BrowerKit request/response instances
1005fd1 fixed Client implementation to return the right Response (closes #4475)