add custom property support for PLY reader ASCII version

git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@1181 fdac6126-5c0c-442c-9429-916003d36597

src/Unittests/TestFiles/cube-minimal-custom_props.ply

@@ -0,0 +1,28 @@
+ply
+format ascii 1.0
+element vertex 8
+property float32 x
+property float32 y
+property float32 z
+property float32 nx
+property float32 ny
+property float32 nz
+property float32 quality
+property uint index
+element face 6
+property list uint8 int32 vertex_indices
+end_header
+-1 -1 -1 0.0  0.0  1.0 1.0 0
+1 -1 -1 0.0  1.0  0.0 0.5 1
+1 1 -1 0.0  1.0  1.0 0.7 2
+-1 1 -1 1.0 0.0  0.0 1.0 3
+-1 -1 1 1.0  0.0  1.0 0.1 4
+1 -1 1 1.0  1.0  0.0 0.0 5
+1 1 1 1.0  1.0  1.0 2.0 6
+-1 1 1 1.0  1.0  2.0 5.0 7
+4 0 1 2 3 
+4 5 4 7 6 
+4 6 2 1 5 
+4 3 7 4 0 
+4 7 3 2 6 
+4 5 1 0 4