Update XSens SDK.
Merge branch 'jabjoe-xsens_update'
XSensMT4: CMake changes to detect libudev
Fix XSens SDK for both Win / Linux

Verified with a MTi-300 in both OSs
fix gcc build
fix xSens build in GCC 4.9 (xsString rewritten as class, not typedef)
Fix build without PbMap (Closes #90)
Fix crash at end of make test for xsens classes
Fix wx string build error in MacOS/clang (Fixes #91)
App DifOdometry-Camera: Bugs fixed
CDifodo: code refactored
OpenNI2 proximity and RGB-D demos: corrections
CSwissRanger3DCamera: bugs fixed
New OpenGL class: CVectorField3D

This class is an OpenGL object consisting of a 3D Vector field. Both the
vector field and the 3D points where this field is evaluated are
specified. Optionally, these points can be shown or not, and the color
of the vector field can be either constant or a linear function of the
vector magnitudes.
CDetectorDoorCrossing  moved to mrpt-detectors

more sensible organization: CDetectorDoorCrossing: mrpt-slam ==>
mrpt::detectors
CPathPlanningMethod  moved to mrpt-nav

CPathPlanningMethod & CPathPlanningCircularRobot: mrpt-slam ==> mrpt-nav
(cont'd)
Fix build errors in GCC
fixed example deps
Eigen: updated to 3.2.2