vtkOBJReader: accept relative indices in OBJ files

Change-Id: I07208e448779486e2947f92fd0baa86d65f566d5
IO/Geometry: add obj index tests

Change-Id: I72d7dcf6e94c692b243dbfbfc156b3ea093a1499
Merge topic 'obj-reader-relative-indices' into master

81ff4519 IO/Geometry: add obj index tests
b11deb8a vtkOBJReader: accept relative indices in OBJ files