Changed the LPC analysis window to an asymetric (pseudo-)Hanning window

so the lookahead necesary is now only 10 ms, making the total algorithmic
delay 30 ms (down from 40 ms).


git-svn-id: http://svn.xiph.org/trunk/speex@3398 0101bb08-14d6-0310-b084-bc0e0c8e3800