Add Triangle method for automatic threshold computation next to the existing
Otsu's method. Triangle deals better with images whose histogram does not
contain dominant peak.

See paper Zack GW, Rogers WE, Latt SA.: Automatic measurement of sister
chromatid exchange frequency. J Histochem Cytochem. 1977 Jul;25(7):741-53.

quickly corrected the previous refactoring of features2d: moved from set(SOME_PROP, val) to setSomeProp(val)

In this particular case t shadows transpose of the base class Matx:
types.hpp:1805:14: warning: declaration of ‘t’ shadows a member of
'this' [-Wshadow]

Changelog gcc 4.8: The option -Wshadow no longer warns if a declaration
shadows a function declaration.

This warning is problematic because it prevents the module
opencv_contrib/modules/ruby to pass the build process

Merge branch 'refactor_features2d_take4' of https://github.com/vpisarev/opencv into refactor_features2d_take4

Conflicts:
	modules/features2d/src/orb.cpp

OpenCV with the refactored features2d compiles! contrib is broken for now; the tests are not tried yet