Merge branch 'gb/maint-submodule-env' into maint

* gb/maint-submodule-env:
is_submodule_modified(): clear environment properly
submodules: ensure clean environment when operating in a submodule
shell setup: clear_local_git_env() function
rev-parse: --local-env-vars option
Refactor list of of repo-local env vars

diff --cc Documentation/git-rev-parse.txt
Simple merge

diff --cc cache.h
Simple merge

diff --cc connect.c
Simple merge

diff --cc git-sh-setup.sh
Simple merge