Use initializer list to create QSet
Don't check what doesn't needs to be checked.
the QBitArray knows how to deal with true / false
directly, so remove the if's. the speedgain of the
if's are probabely slower than just setting the values
to true / false again anyway as we are not suffering
from a possible branch-prediction, and plus, code is
cleaner.
No need to test for true / false to set true false
Just set it directly