Dealing git ignored files

Hi,

I developed a custom tool git-ignore to deal with different
buildsystems and developing.

I start it as a helper, really not knowing how useful it will be but
it end being used in any project at some moment (ignoring autotools in
source tree generated files, excluding test generated files, excluding
temp files, ignoring build directories...)

git ignore _build/
git ignore target/
git ignore -i Makefile.in
git ignore -i '*.o' -x dist/

It offers man page, help and autocompletion so:

git ignore --help
git ignore -h
git ignore <tab>

all work as would be expected for any git command

If offers an easy access to `./git/info/excluded` `.gitignore` with:

git ignore -e
git ignore -i -e

Which could fill a gap dealing with this files as `git config` does
with config files

It is maintained under autotools and use sharness as test suite, so It
pretty much mimic the git workflow.

I'm sure it can be improved in several ways, but do you think it is
something that can be added to the standard git tooling?

Any feedback would be appreciated, issue tracker is open to missing features:

https://github.com/albfan/git-ignore/issues

Cheers,
Alberto