- a linear float buffer was being created and saved into a non-linear DPX/Cineon file.
- removed the UI since the settings are not used at the moment.
added a utility function IMB_float_profile_ensure(), which returns a float buffer in the requested profile, using the existing if needed or returning an allocated buffer if the profile is different to that of the ImBuf. - Useful this case where the save function has its own linear setting.