Confirm better to autotools, because of that no need to use lseek64
anymore and also no need to use O_LARGEFILE.

This fixes opening of "large" files (> 4 Gb).
Enable seeking in "difficult" files (when there is a "tail"
with a "PCR" pid that doesn't actually have PCR fields), as
observed on a recording from BBC One HD.

There is still no support for seeking in files that have a
PCR wraparound.
Minor/cosmetic.