Merge branch 'upstream/develop'
Merge branch 'upstream/master'
Added new Matrix33 constructor and test functions.

Added a new ChMatrix33 constructor which builds a diagonal matrix with
same elements on the diagonal (useful to construct an identity 3x3 matrix).
Added two utility functions which test if a 3x3 matrix is the identity matrix
and if a vector is the null vector, respectively.
Declare a couple of ChMatrix33 and ChVector methods as const.

More such changes should be done.  These are the ones required for
the changes to the ChCollisionModel::Add***() function prototypes.
Clean up prototypes for the ChCollisionModel::Add***() functions.

Modified the prototypes of all functions used to specify collision
geometry so that they take const refs to the position and orientation
of the contact shapes (instead of pointers to a ChVector and ChMatrix33,
respectively).

This cleans up the code and addresses compilation warnings regarding
'taking address of temporary' (gcc) or 'class rvalue used as lvalue' (cl).
Update demos to reflect changes in ChCollisionModel::Add***() functions.

Pass position and orientation matrix for contact shapes as const refs, not
pointers.
Fix a couple of 'multiple defintion' linker warnings.

Move defintions of static functions from the header file to the source file
so that these functions are not multiply-defined.
Fix bug in implementation of ChMatrix33::IsIdentity()
Enable full RPATH linking for installed executables

By default, CMake links executables with full RPATH only in the build tree and
clears the RPATH before installing targets.  This means that, by default, installed
executables will not find the shared libraries (unless these are installed in a default
location, such as /usr/local/lib).

With this change (lifted directly from the CMake wiki), executables are relinked with
the install RPATH.  This allows running the installed executables regardless of the
installation location and without having to change LD_LIBRARY_PATH.
Merge branch 'master' of https://github.com/rserban/chrono into develop

Conflicts:
	src/unit_FEM/ChPolarDecomposition.h
Resolved conflict using rserban approach.