gtStrainPlaneNormals: now also outputs the reference vectors

Signed-off-by: preischig <preischig@gmail.com>

zUtil_Strain2/gtStrainPlaneNormals.m

-function [pldef, drel] = gtStrainPlaneNormals(pl, defT)
+function [pldef, drel, e1, e2] = gtStrainPlaneNormals(pl, defT)
 % GTSTRAINPLANENORMALS Given a deformation tensor, calculates new plane 
 % normals with no approximations.
 % 
@@ -17,8 +17,10 @@ function [pldef, drel] = gtStrainPlaneNormals(pl, defT)
 %   defT  - deformation tensor(s) (3x3 or 3x3xn)
 %
 % OUTPUT
-%   pldef - plane normals in deformed state
-%   drel  - relative elongations along the (deformed) plane normals
+%   pldef - plane normals in deformed state (3xn)
+%   drel  - relative elongations along the (deformed) plane normals (1xn)
+%   e1    - reference vectors 1, perpendicular to pl; not normalised; (3xn)
+%   e2    - reference vectors 2, perpendicular to pl and e1; not normalised; (3xn)
 %
 
 num_pls = size(pl, 2);