[Seaside-dev] The new way to generate session ids

[Philippe Marschall]

Hi

During the Seaside sprint at Konstanz we made the following changes to
the session and continuation key generation mechanism:
- Session and continuation keys are always Strings, that removes a lot
of conversion code.
- WAExternalID has been replaced by WAKeyGenerator with generates this String.
- SeasidePlatformSupport class >> #randomClass has been replaced by
#newRandom. This method is supposed the random number generator used
by WAKeyGenerator go generate the random numbers. The only method sent
to it is #nextInt:. However you have to make sure this method is
thread safe works in a load balanced scenario.

Cheers
Philippe