Merge branch 'ld/discovery-limit-to-fs' (early part)

* 'ld/discovery-limit-to-fs' (early part):
  Rename ONE_FILESYSTEM to DISCOVERY_ACROSS_FILESYSTEM
  GIT_ONE_FILESYSTEM: flip the default to stop at filesystem boundaries
  Add support for GIT_ONE_FILESYSTEM
  truncate cwd string before printing error message
  config.c: remove static keyword from git_env_bool()

diff --cc Documentation/git.txt
Simple merge

diff --cc cache.h
Simple merge

diff --cc config.c
Simple merge