Merge branch 'jg/status-config'

Merge branch 'jg/status-config'

"git status" learned status.branch and status.short configuration
variables to use --branch and --short options by default (override
with --no-branch and --no-short options from the command line).

* jg/status-config:
  status/commit: make sure --porcelain is not affected by user-facing config
  commit: make it work with status.short
  status: introduce status.branch to enable --branch by default
  status: introduce status.short to enable --short by default