installed DimensionOfAmbientSpace for IsAlgebraicThomasDecompositionSchemeRp
support constructible sets and QuasiAffineDecomposition

. renamed and generalized the low-level constructor ...
. fixed several boolian operators
. declared and installed QuasiAffineDecomposition
. fixed example (IsQuasiAffine -> IsQuasiAffineSubscheme, ... )

(needs Sheaves 2013.07.10)