Bugfixes regarding selectable rows

- win_goto_top and friends now respect the selectable property of rows.
- Moved code to select a selectable row after window_set_contents to
  window_set_contents.
- Also some comment style fixes.
Merge pull request #79 from mahkoh/show-all-tracks

Bugfixes regarding selectable rows
ignore releaseDate=0 in mp4 files
Merge pull request #81 from mahkoh/m4a

ignore releaseDate=0 in mp4 files
use mp4 genreType if necessary
Merge pull request #82 from mahkoh/mp4tags

use mp4 genreType if necessary