Merge branch 'ab/repo-settings-cleanup'

Code cleanup.

* ab/repo-settings-cleanup:
  repository.h: don't use a mix of int and bitfields
  repo-settings.c: simplify the setup
  read-cache & fetch-negotiator: check "enum" values in switch()
  environment.c: remove test-specific "ignore_untracked..." variable
  wrapper.c: add x{un,}setenv(), and use xsetenv() in environment.c

diff --cc cache.h
Simple merge

diff --cc environment.c
Simple merge

diff --cc git-compat-util.h
Simple merge

diff --cc read-cache.c
Simple merge

diff --cc repository.h
Simple merge