[edl] switch to int (we're dealing with ms, which gives us +/- 600 hours for the cut points
use size_t for iteration to save casts
fixes various warnings about unsigned/signed, float/int etc.
[cosmetic] make a bunch of Edl functions const
[cosmetic] drop unused functions for mplayer Edl writing
Merge pull request #4917 from jmarshallnz/rwarnings

Fix a bunch of warnings