[patch] Add reference for one project.

[Edward Jason Riedy]

Just adding a reference to one of Dr. Kahan's papers about complex
arithmetic.  He gives routines / formulae that could be used for
the complex mappers.

Jason

        * PROJECTS: Add reference for complex mapper functions.

--- ../CVS-srcs/octave/PROJECTS Thu Jan 20 23:48:26 2000
+++ PROJECTS    Wed Aug 16 15:41:58 2000
@@ -23,7 +23,11 @@
 
   * Improve logm, and sqrtm.
 
-  * Improve complex mapper functions.
+  * Improve complex mapper functions.  See W. Kahan, ``Branch Cuts for
+    Complex Elementary Functions, or Much Ado About Nothing's Sign
+    Bit'' (in The State of the Art in Numerical Analysis, eds. Iserles
+    and Powell, Clarendon Press, Oxford, 1987) for explicit
+    trigonometric formulae.
 
   * Make functions like gamma() return the right IEEE Inf or NaN
     values for extreme args or other undefined cases.