Blender Git Loki

ImBuf: Made Wrapping and Cropping optional in IMB_transform.

`IMB_transform` is used in VSE. It had a required crop parameter
for cropping the source buffer. This is not always needed.

In the image engine we want to use the use the `IMB_transform`
with wrap repeat. Both options are mutual exclusive and due
to performance reasons the wrap repeat is only available when
performing a nearest interpolation.