tests: replace test_tristate with "git env--helper"

The test_tristate helper introduced in 83d842dc8c ("tests: turn on
network daemon tests by default", 2014-02-10) can now be better
implemented with "git env--helper" to give the variables in question
the standard boolean behavior.

The reason for the "tristate" was to have all of false/true/auto,
where "auto" meant either "false" or "true" depending on what the
fallback was. With the --default option to "git env--helper" we can
simply have e.g. GIT_TEST_HTTPD where we know if it's true because the
user asked explicitly ("true"), or true implicitly ("auto").

This breaks backwards compatibility for explicitly setting "auto" for
these variables, but I don't think anyone cares. That was always
intended to be internal.

This means the test_normalize_bool() code in test-lib-functions.sh
goes away in addition to test_tristate(). We still need the
test_skip_or_die() helper, but now it takes the variable name instead
of the value, and uses "git env--bool" to distinguish a default "true"
from an explicit "true" (in those "explicit true" cases we want to
fail the test in question).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-git-svn.sh

@@ -69,14 +69,12 @@ svn_cmd () {
 maybe_start_httpd () {
 	loc=${1-svn}
 
-	test_tristate GIT_SVN_TEST_HTTPD
-	case $GIT_SVN_TEST_HTTPD in
-	true)
+	if git env--helper --type=bool --default=false --exit-code GIT_TEST_HTTPD
+	then
 		. "$TEST_DIRECTORY"/lib-httpd.sh
 		LIB_HTTPD_SVN="$loc"
 		start_httpd
-		;;
-	esac
+	fi
 }
 
 convert_to_rev_db () {
@@ -106,8 +104,7 @@ EOF
 }
 
 require_svnserve () {
-	test_tristate GIT_TEST_SVNSERVE
-	if ! test "$GIT_TEST_SVNSERVE" = true
+	if ! git env--helper --type=bool --default=false --exit-code GIT_TEST_SVNSERVE
 	then
 		skip_all='skipping svnserve test. (set $GIT_TEST_SVNSERVE to enable)'
 		test_done