Bug#558733:

[Mathieu Malaterre]

Recent posting also mention to use the latest release candidate as a release:

http://www.asmail.be/msg0054536609.html

...
The code is in fairly wide production use, but for various
reasons we have had trouble making the transition to a
libtiff 4 final release.  So my advice is go ahead an use
it as if the latest alpha/beta is a ready release.

Note that the latest release is at:

  http://download.osgeo.org/libtiff/

and is 4.0.0beta7
...