test-lib: make BAIL_OUT() work in tests and prereq

BAIL_OUT() is meant to abort the whole test run and print a message with
a standard prefix that can be parsed to stdout. Since for every test the
normal fd`s are redirected in test_eval_ this output would not be seen
when used within the context of a test or prereq like we do in
test_have_prereq(). To make this function work in these contexts we move
the setup of the fd aliases a few lines up before the first use of
BAIL_OUT() and then have this function always print to the alias.

Signed-off-by: Fabian Stelzer <fs@gigacodes.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -589,6 +589,15 @@ USER_TERM="$TERM"
 TERM=dumb
 export TERM USER_TERM
 
+# What is written by tests to stdout and stderr is sent to different places
+# depending on the test mode (e.g. /dev/null in non-verbose mode, piped to tee
+# with --tee option, etc.). We save the original stdin to FD #6 and stdout and
+# stderr to #5 and #7, so that the test framework can use them (e.g. for
+# printing errors within the test framework) independently of the test mode.
+exec 5>&1
+exec 6<&0
+exec 7>&2
+
 _error_exit () {
 	finalize_junit_xml
 	GIT_EXIT_OK=t
@@ -612,7 +621,7 @@ BAIL_OUT () {
 	local bail_out="Bail out! "
 	local message="$1"
 
-	say_color error $bail_out "$message"
+	say_color >&5 error $bail_out "$message"
 	_error_exit
 }
 
@@ -637,9 +646,6 @@ then
 	exit 0
 fi
 
-exec 5>&1
-exec 6<&0
-exec 7>&2
 if test "$verbose_log" = "t"
 then
 	exec 3>>"$GIT_TEST_TEE_OUTPUT_FILE" 4>&3