Sync with 2.17.2

Sync with 2.17.2

* maint-2.17:
  Git 2.17.2
  fsck: detect submodule paths starting with dash
  fsck: detect submodule urls starting with dash
  Git 2.16.5
  Git 2.15.3
  Git 2.14.5
  submodule-config: ban submodule paths that start with a dash
  submodule-config: ban submodule urls that start with dash
  submodule--helper: use "--" to signal end of clone options