Get /.gitignore from master branch

.gitignore from 13744e0412652f497a5a79283a24e54aa630a00d (latest change of
the file on the 'master' branch).
Cherry-picking was not possible because the commits concerned other files
than .gitignore.
Merge pull request #191 from dolmen/msys-gitignore

MSYS branch: get /.gitignore from master branch