added documentation for ORB (ticket #1835). updated documentation on features2d (Feature2D class is still to be documented) (ticket #1819)

decreased the number of tests in Core_Eigen, decreased the maximum matrix size in Core_SVD; now those tests take less time to complete

Minor improvements: reduced verbosity of positioning tests; run.py - filter out non-executables on windows

modified data matrix detection interface (that does not use any new data structures). Added Python sample for data matrix detection. Ticket #1664

put template Distance classes back to features2d, since they are used in GPU; fixed OpenCV build with Xcode 2.3 (which includes new libpng)

added BruteForceMatcher (the older variant of BFMatcher) to legacy (ticket #1796). added test for it. Renamed legacy tests to "Legacy_*"