Merge branch 'jk/maint-pass-c-config-in-env'

* jk/maint-pass-c-config-in-env:
  do not pass "git -c foo=bar" params to transport helpers
  pass "git -c foo=bar" params through environment

diff --cc cache.h
Simple merge

diff --cc environment.c
Simple merge

diff --cc git.c
Simple merge