[Debug] Handled errors
feature #10725 [Debug] Handled errors (nicolas-grekas)

This PR was squashed before being merged into the 2.5-dev branch (closes #10725).

Discussion
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[Debug] Handled errors

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | none
| License       | MIT
| Doc PR        | none

Enhance error handling and thus displaying for catchable PHP errors.
Code is tricky thanks to https://bugs.php.net/54275

Before:

![capture du 2014-04-17 10 03 40](https://cloud.githubusercontent.com/assets/243674/2729324/4de3eedc-c607-11e3-8b23-c88657bbecd0.png)

After:

![capture du 2014-04-17 10 03 14](https://cloud.githubusercontent.com/assets/243674/2729326/534ec504-c607-11e3-82dd-49b7770b1e75.png)

Commits
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0279fbf [Debug] Handled errors