Update Session.php

Fixed a problem that caused multiple RPC calls from the same client to get wrong responses.
Update Session.php

Fixed methods so getUniqueId returns numbers according to WAMP specs.
Update Session.php

Refactoring of methods creating id
make unique ids more unique
Merge branch 'pantsel'

# By Tselentis (3) and Matt Bonneau (1)
* pantsel:
  make unique ids more unique
  Update Session.php
  Update Session.php
  Update Session.php