[Proj] Inverse Winkel Tripel and others

[Gerald I. Evenden]

After sleeping on the problem for a bit and enjoying the services of my new 
toy introduced in the tmerc circus I am now of the opinion that GSL is 
probably not needed in inversing inverseless projections.

However, libproj4 will need one or two tweeks to lib_proj.h and introduction 
of a new support routine.  I suspect the changes will warrant a boost of the 
release number from 4.3 to 4.4.  If the methods I now envision works, it will 
still take some time to apply it to all the inverse-less projections; even 
then some will probably remain inverse-less.  Worry about that later.

I will use Winkel Tripel as the first development/test case.

-- 
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist