Manage variadic arguments.
Test should be executed only for PHP ≥ 5.6.
Class with variadic argument should be compiled at runtime to avoid parse error with PHP version ≤ 5.6.
Factor some code
Merge pull request #6 from jubianchi/newTestedInstanceWithVariadic

Factor some code to avoid code duplication, thanks to @jubianchi.
Merge pull request #379 from mageekguy/newTestedInstanceWithVariadic

Fix `newTestedInstance` assertion when constructor contains an ellipsis