Update qbs submodule.

And do the necessary adaptation in the Qbs project manager, namely
giving the qbs::Settings object a base directory. The respective change
in the qbs API is necessary for being able to run more than one QtC
instance at the same time without ill effects.

Change-Id: I6859a6616bd744915aa21c3f07b6c45243899de5
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>