fix tlm support

[jcupitt]

tlm needs target rewrite

see #5

[jcupitt]

Test with eg.:

$ vips kakadusave k2.jpg x.jp2 --options "Qfactor=90 Cmodes=HT ORGgen_plt=yes Creversible=no Cblk={64,64} ORGtparts=R ORGgen_tlm=9"

** (vips:38242): WARNING **: 17:23:15.321: Kakadu Core Warning:
The `Qweights' parameter values supplied are not a close match to the
square-root of the synthesis energy gains of the prevailing multi-component
transform, if any, in tile 0.  Use the following parameters: 1.732051,
1.805108, 1.573402.

There's a test in the test suite too.

[scossu]

This seems to work now—at least it creates a JP2 with no warning. Do you know how I can inspect the image for the TLM marker?

[jcupitt]

Sorry, I'm not sure. You can see that the bytes in the file change with this option, maybe that's enough?

[scossu]

I guess we'll merge this in for now, maybe I can ask the Kakadu devs if there are specific metadata flags to detect these features.