Add a preview to _forgit_clean

[sandr01d]

Check list

• [X] I have performed a self-review of my code
• [ ] I have commented my code in hard-to-understand areas
• [X] I have made corresponding changes to the documentation

Description

gclean is the only command that does not display a preview. I sometimes find myself exiting gclean just to check the content of a file before deleting it. Being able to have a last peek at a file before removing it does sound like a good idea in general to me.

Type of change

• [ ] Bug fix
• [X] New feature
• [ ] Refactor
• [ ] Breaking change
• [ ] Documentation change

Test environment

• Shell
  • [X] bash
  • [X] zsh
  • [ ] fish
• OS
  • [X] Linux
  • [ ] Mac OS X
  • [ ] Windows
  • [ ] Others:

[sandr01d]

FYI: I've added a preview for directories now as well (before this you'd see an unwanted error message when trying to preview a directory). Looks like this when tree is installed

Otherwise like this:

Feel free to give this another review if you like. Will keep testing this for a few days.