VAO wrapper doesn't play well with padded format strings

[einarf]

When the user provides a format string with nxn it doesn't know how to hande it properly. It also doesn't handle cases were the number of formats are not the same as attributes. 3f 8x4 should be acceptable for one attribute because the second format simply expresses an offset to stride.

This must work for normal attributes and instance data. There is something fishy happening when using padding in instance data as well.

[einarf]

Note: We can also use Program.detect_format in 5.6.