adding support for additional elements in PLY files
This patch handles PLY files with additional elements besides 'vertex' and 'face'. Currently files containing additional elements before 'face' will result in undefined behavior of PLYReader for example if the extra data is read instead of the actual face data a wrong number of indices is read and not handled gracefully.
The changes made will handle the situation by correctly reading (and disposing) any additional elements besides 'vertex' and 'face'.
An example handled by this patch would be a file with the following header:
ply format ascii 1.0 comment this file contains extra elements element vertex 8 property float x property float y property float z element extra_element 4 property float a property float b property float c element face 6 property list uchar int vertex_index end_header