All new LSP->freq envelope curve computation code.

It turns out that LSP->LPC using the impulse response algorithm is
*very* sensitive to noise, and doubles really are necessary.
Unfortunate, that.

Reimplmented the code with a direct LSP->curve computation, skipping
the LPC intermediary step.  This also eliminates any need for the LPC
or iFFT code in decode/synthesis.

Monty

svn path=/trunk/vorbis/; revision=597