Implement trig functions in Lisp

 code/irrat.lisp::
 * Add Lisp implementation for sin, cos, and tan, based on code from
   fdlibm.  Requires the C reduction routines.  Only working so far on
   systems that already include the reduction routies.

 tests/trig.lisp::
 * Tests for the new sin, cos, and tan functions.  Tests pass on
   x86/darwin.