Generalized Lambert W function - premature commit



Oops. I have accidentally committed some code for Generalized Lambert W function to src/specfn.lisp.  Still getting my head around git.

commit a6bbd00cabe41aa429f46b268a8c6a7f086e53b3
Author: David Billinghurst<dbmaxima at gmail.com>
Date:   Mon May 14 23:12:07 2012 +1000

The code seems functionally correct, and passes tests in tests/rtest_lambert_w.mac, but I hadn't finished polishing it and it is still undocumented.  Unless anyone objects, I will leave it in place for the time being.

There is a new function generalized_lambert_w(k,z) that returns the kth branch W_k(z).  There are float and bigfloat routines for complex z.  generalized_lambert_w(0,z) is not (yet) simplified to lambert_w(z), as I hadn't decided if this should be done unconditionally or controlled by a flag.  Thoughts?