This ports the prompts that actually used __fish_git_prompt to a new function __fish_vcs_prompt that just calls all shipped vcs prompts.
This should close #2431.
The remaining questions are:
CC @siecje, @derekstavis.
This also touches #2582, which should also be added to __fish_vcs_prompt once it's merged.
Add __fish_vcs_prompt helper function
This is supposed to be used by prompts so they'll get all known vcsen
For now, there's no distinction between the different vcsen.
Switch classic + git prompt to all vcsen
Keep the name as that's used in variables.
Make lonetwin prompt use __fish_vcs_prompt
Make informative_git prompt use vcs_prompt
Add svn to __fish_vcs_prompt
Update makepkg completion
A few options were missing and --asroot has been removed
Merged as baa6971..482cfca.