renamed variables - making next change more readable
reduced recursion when building DumperPrefixCollection
bug #10215 [Routing] reduced recursion in dumper (arnaud-lb)

This PR was submitted for the 2.3-dev branch but it was merged into the 2.3 branch instead (closes #10215).

Discussion
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[Routing] reduced recursion in dumper

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | sensiolabs/SensioFrameworkExtraBundle/issues/275
| License       | MIT

This reduces recursion in the route dumper, avoiding issues with xdebug's recursion limit.

Commits
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fa6eebc reduced recursion when building DumperPrefixCollection
9278b27 renamed variables - making next change more readable