Merge branch 'jk/bug-to-abort' into maint

Introduce the BUG() macro to improve die("BUG: ...").

* jk/bug-to-abort:
usage: add NORETURN to BUG() function definitions
config: complain about --local outside of a git repo
setup_git_env: convert die("BUG") to BUG()
usage.c: add BUG() function