Clean up and polish the port:

- Remove DPB_PROPERTIES. It breaks the doc. We need TLS.

- Change references to pixman. I still not sure if the bug is in pixman
  or cairo.

- Remove slow mirror and add the url of prereleases.

- Drop GCC 4.6. I was using GCC 4.6 due to the "emulated" TLS support
  but this is only adding bugs. I prefer release the port only with
  features 100% safe and tested.

- Disable "places" and "futures", both require TLS.

- Enhance some comments.

- Add again the PFRAG trick for doc related to images.

- Remove unnecessary patch.

- Enhance README.
Remove TODO.