Merge pull request #128 from thocevar/tree

Added sklearn tree tests.
Improve test (avoid non-deterministic results).
Indices should be integers.
Test Learners widget (Orange.evaluation.testing.CrossValidation) calls StratifiedKFold.
Minor.
Minor.
Allow for minimal fold index start/stop differences.
Fix test.
Merge pull request #131 from tomazc/test_learners

Test Learners widget (evaluation.testing.CrossValidation) calls StratifiedKFold.
Fix a bug in tab reader.

Values were shifted in lines that began with an unknown value.
Added PCA widget.
Add Classification tree widget
Add icon and fix signal types and handlers for classification tree widget
Tree widgets constructs the learner/classifier and sends it
Weights are optional.
Move init and predict to SklFitter base class.
Merge pull request #135 from lanzagar/sklfitter

Move functionality to SklFitter base class.
Fixed incorrectly generated code by cython.
Merge pull request #129 from janezd/classification-tree

Add Classification tree widget
Merge pull request #136 from thocevar/cython

Fixed incorrectly generated code by cython (BasketReader).