Commit some build file changes, remove .gitignore

Any time files are added or removed to Cinnamon, and the makefiles are updated, many of us have problems building, and need to run autogen (even though it should be run automatically) one time, to fix things.

We really shouldn't be ignoring all these generated files, we should be removing them before building, yet they should not stand in our way of making and committing changes.

So we should remove .gitignore, that way all these autogenerated files can be blown away with:

    git clean -fd

And they're all gone, back to a clean working source.

If you make changes to code, you can still just do:

    git commit -a

And it will pull in only modified files, not untracked, so you can keep a make-ready source tree while working on things, and the untracked files won't interfere with your commits.

This is how Nemo works, and it's quite efficient and easy to manage.