Merge branch 'nd/clear-gitenv-upon-use-of-alias'

Merge branch 'nd/clear-gitenv-upon-use-of-alias'

d95138e6 (setup: set env $GIT_WORK_TREE when work tree is set, like
$GIT_DIR, 2015-06-26) attempted to work around a glitch in alias
handling by overwriting GIT_WORK_TREE environment variable to
affect subprocesses when set_git_work_tree() gets called, which
resulted in a rather unpleasant regression to "clone" and "init".
Try to address the same issue by always restoring the environment
and respawning the real underlying command when handling alias.

* nd/clear-gitenv-upon-use-of-alias:
  run-command: don't warn on SIGPIPE deaths
  git.c: make sure we do not leak GIT_* to alias scripts
  setup.c: re-fix d95138e (setup: set env $GIT_WORK_TREE when ..
  git.c: make it clear save_env() is for alias handling only