fd should respect GIT_CEILING_DIRECTORIES

[stweller]

In newer git versions, GIT_CEILING_DIRECTORIES can be used to make sure git doesn't look for .gitignore files outside e.g. a users home. In setups where an NFS automounter works on some parent directory of the users home, just looking for .gitignore can mean a significant slowdown (some seconds, not just milliseconds). It would be great if fd could also respect this setting.

The behavior of git itself with respect to GIT_CEILING_DIRECTORIES is described here.