tests: Fix race condition in t7006-pager

Pagers that do not consume their input are dangerous: for example,

 $ GIT_PAGER=: git log
 $ echo $?
 141
 $

The only reason these tests were able to work before was that
'git log' would write to the pipe (and not fill it) before the
pager had time to terminate and close the pipe.

Fix it by using a program that consumes its input, namely wc (as
suggested by Johannes).

Reported-by: Johannes Sixt <j.sixt@viscovery.net>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7006-pager.sh

@@ -137,7 +137,7 @@ rm -f default_pager_used
 test_expect_success SIMPLEPAGER 'default pager is used by default' '
 	cat > $less <<-EOF &&
 	#!$SHELL_PATH
-	: > default_pager_used
+	wc > default_pager_used
 	EOF
 	chmod +x $less &&
 	PATH=.:$PATH test_terminal git log &&
@@ -148,7 +148,7 @@ unset GIT_PAGER
 git config --unset core.pager
 rm -f PAGER_used
 test_expect_success TTY 'PAGER overrides default pager' '
-	PAGER=": > PAGER_used" &&
+	PAGER="wc > PAGER_used" &&
 	export PAGER &&
 	test_terminal git log &&
 	test -e PAGER_used
@@ -157,17 +157,17 @@ test_expect_success TTY 'PAGER overrides default pager' '
 unset GIT_PAGER
 rm -f core.pager_used
 test_expect_success TTY 'core.pager overrides PAGER' '
-	PAGER=: &&
+	PAGER=wc &&
 	export PAGER &&
-	git config core.pager ": > core.pager_used" &&
+	git config core.pager "wc > core.pager_used" &&
 	test_terminal git log &&
 	test -e core.pager_used
 '
 
 rm -f GIT_PAGER_used
 test_expect_success TTY 'GIT_PAGER overrides core.pager' '
-	git config core.pager : &&
-	GIT_PAGER=": > GIT_PAGER_used" &&
+	git config core.pager wc &&
+	GIT_PAGER="wc > GIT_PAGER_used" &&
 	export GIT_PAGER &&
 	test_terminal git log &&
 	test -e GIT_PAGER_used