Merge branch 'ab/test-env'
Many GIT_TEST_* environment variables control various aspects of
how our tests are run, but a few followed "non-empty is true, empty
or unset is false" while others followed the usual "there are a few
ways to spell true, like yes, on, etc., and also ways to spell
false, like no, off, etc." convention.
env--helper: mark a file-local symbol as static
tests: make GIT_TEST_FAIL_PREREQS a boolean
tests: replace test_tristate with "git env--helper"
tests README: re-flow a previously changed paragraph
tests: make GIT_TEST_GETTEXT_POISON a boolean
t6040 test: stop using global "script" variable
config.c: refactor die_bad_number() to not call gettext() early
env--helper: new undocumented builtin wrapping git_env_*()
config tests: simplify include cycle test