minor #490 Fix PSR4 in composer.json, add dump() (nicolas-grekas)

This PR was merged into the master branch.

Discussion
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Fix PSR4 in composer.json, add dump()

Empty psr-4 prefixes can force the autoloader to scan the `src/` directory for all namespaces. The best practice is to always have make the prefix explicit.

`composer update` also, doing:
```
  - Updating twig/twig (v1.31.0 => v1.32.0) Loading from cache
  - Updating sensiolabs/security-checker (v4.0.0 => v4.0.1) Loading from cache
  - Updating phpunit/php-timer (1.0.8 => 1.0.9) Loading from cache
  - Updating phpunit/php-token-stream (1.4.9 => 1.4.11) Loading from cache
```

Commits
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3adc0b9 Fix PSR4 in composer.json, add dump()

composer.json

@@ -4,11 +4,15 @@
     "type": "project",
     "description": "Symfony Demo Application",
     "autoload": {
-        "psr-4": { "": "src/" },
+        "psr-4": {
+            "AppBundle\\": "src/AppBundle/",
+            "CodeExplorerBundle\\": "src/CodeExplorerBundle/"
+        },
         "classmap": [ "app/AppKernel.php", "app/AppCache.php" ]
     },
     "autoload-dev": {
-        "psr-4": { "Tests\\": "tests/" }
+        "psr-4": { "Tests\\": "tests/" },
+        "files": [ "vendor/symfony/symfony/src/Symfony/Component/VarDumper/Resources/functions/dump.php" ]
     },
     "require": {
         "php"                                  : ">=5.5.9",