Warn when trying to commit files that should be tracked in LFS

[andresovela]

I found out today that gitui does not yet support git lfs (#1089).

Today I pushed a large file by accident because I didn't realize gitui wouldn't do the expected thing. It'd be nice if gitui warned about adding/committing files tracked in LFS as long as LFS is not supported.

A short "this file is tracked in LFS but gitui does not support it yet - add this file manually using git" would prevent this from happening :)

[extrawurst]

Wonder how we can programmatically figure that out

[andresovela]

The .gitattributes file has something like this:

*.iso filter=lfs diff=lfs merge=lfs -text

I guess it's just a matter of issuing a warning on all .iso files then, or whatever the rule is