git may create .orig versions of files when running mergetool. These files then...

git may create .orig versions of files when running mergetool.  These files then become suggested additions because they are not ignored by .gitignore.

The ways to handle this are
+ add *.orig to .gitignore
+ change a git config to not generate backup files
+ rm them by hand
+ try to ignore them visually

It can be useful to have a backup of a file in case the merge, um, goes poorly (pilot error, for example).  It's cumbersome to rm them or ignore them visually.

Let's add *.orig to the root .gitignore.

BUG=

Review URL: https://codereview.chromium.org/995153002

Cr-Commit-Position: refs/heads/master@{#320006}