sample code : https://github.com/Itseez/opencv/blob/master/samples/cpp/tutorial_code/features2D/SURF_descriptor.cpp

Bug #2888

OpenCV Manager verison incremeneted;
Docs and tests updated accordingly;
COnstant for Manager initialization added.

Old paths can have problems with cross-compilation

Native activity build warning fixed;
Logcat messages for JavaCameraView updated (Bug #2876);
Some fixes for feature #2893 done.

Issue #2868

Based on pull request #685

Issue #2820

Set ptr to NULL, so this method can be called repeatedly. This fixes a crash after unplugging web cam and trying to re-scan the cameras.