Would write 1.04 seconds as `00:00:01,40` instead of `00:00:01,040`...
Anyway, we already have BLI API for timecodes, much better to add
SubRip timecode format there, heavily simplifies code.
To be backported to final 2.76.
- deduplicate timecode_simple_string from image.c
- replace V2D_UNIT_SECONDSSEQ with V2D_UNIT_SECONDS
- avoid possible buffer overflow bugs (sprintf -> BLI_snprintf)
- remove option not to use timecode and split into 2 functions
Patch D227 by Andrew Buttery with own refactoring.
