Fixes for clang compiler support.

Added 'TOrangeVector::classDescription()' specialization to
'DEFINE_TOrangeVector_classDescription' macro and removed its default implementation
in the template class (static 'st_classDescription' member must be initialized/specialized before
its use).

A similar problem arises in the included '.ppp' files where st_classDescription is used. So I
moved all '.ppp. includes after the "DEFINE_*"s.

Removed unnecessary/duplicate VWRAPPER/WRAPPER uses.

Added 'this->...' qualifier in template classes (that inherit a from a template class) for
accessing base class methods, otherwise clang does not find them (as per C++ standard).

Moved the TVarList and TAttributed*List definitions/implementations from 'orvector' to 'vars'.
Fixed includes in other files using the two headers accordingly.

Fixed some casts to int with more appropriate casts to size_t/uintptr_t.

Added explicit casts of constants to template class in include/stat.hpp
statistics functions.

(references #1219).
Fixed Linear Regression widget's parameters for Lasso regression.
Minor changes in Orange.data.Table documentation.
Set the 'distribution.variable' in BaggingClassifier and ProbabilityEstimator_loess

The retured distribution of BaggedClassifier.__call__ would raise an
'invalid distribution (no variable)' when calling '.items()', Similary any
classifier where ProbabilityEstimator_loess can be used (for instance
MajorityClassifier).
Test that the returned distribution has the proper variable (class_var).
Set distribution variable in 'SimpleTreeLearner.classDistribution'.
Replaced 'OWReport.report' references with 'OWReport.get_instance()'.

This returns 'qApp.canvasDlg.reportWindow' if present (see #1226).
Scoring additions, preparation for Clustering Trees and multi-target addon
Added Clustering Trees to Orange.core
Fixes to unit-tests
Additional fixes and source modifications
Added NeuralNetworkClassifier, removed a multitarget reference in docs
C++ Windows daily build fix
Added numpydoc requirement.
Removed multitarget imports from __init__.py
trivial merge
Fixed failing test
Version bump
Added tag 2.6a2 for changeset 69c197e609e8
Fixed a typo in OWDatabasesUpdate.