PR: fix bc break in PHP_Parser <0.9.2

When using other bundles like "JMS/TranslationBundle" who require php_parser = v0.9.1, Sami breaks.

They changed their api as you can see here: https://raw.github.com/nikic/PHP-Parser/master/CHANGELOG.md  changelog v0.9.2: [BC] Use inject-once approach for lexer.

I found no way to check for the package it's version so i wrapped it around a try catch. If anyone has a better solution feel free to add.