src/flac/main.c : Fix an output line > 81 characters in length.

Requested-by: lvqcl <lvqcl.mail@gmail.com>
Improve encoding speed on older Intel CPUs.

The commit http://git.xiph.org/?p=flac.git;a=commit;h=e9d805dd4374
changed the that calculate autocorrelation. However, the new code
worked slightly (about 4%) slower on Core 2, but with the new
presets the speed decrease can reach ~25%.

This patch enables both old and new functions and chooses between
them at runtime.

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