flac : Add help output for --ignore-chunk-sizes option.

Patch-from: lvqcl <lvqcl.mail@gmail.com>
stream_encoder.c : Give the encoder a larger stdio buffer.

Windows in particular can experience slow encoding speeds on highly
fragmented disks. Using setvbuf to increase the size of the buffer to
10Meg.

This is probably not needed on Linux/Unix, but is very unlikely to
to cause any negative effects.

Patch-from: Janne Hyvärinen <cse@sci.fi>
libFLAC/cpu.c : Refactor for readability.

Patch-from: lvqcl <lvqcl.mail@gmail.com>