Merge branch 'jl/submodule-ignore-diff'

* jl/submodule-ignore-diff: Add tests for the diff.ignoreSubmodules config option Add the 'diff.ignoreSubmodules' config setting Submodules: Use "ignore" settings from .gitmodules too for diff and status Submodules: Add the new "ignore" config option for diff and status Conflicts: diff.c