t/lib-httpd: refactor "one-time-perl" CGI script to not depend on Perl

Our Apache HTTPD setup exposes an "one_time_perl" endpoint to access
repositories. If used, we execute the "apply-one-time-perl.sh" CGI
script that checks whether we have a "one-time-perl" script. If so, that
script gets executed so that it can munge what would be served. Once
done, the script gets removed so that it doesn't execute a second time.

As the name says, this functionality expects the user to pass a Perl
script. This isn't really necessary though: we can just as easily
implement the same thing with arbitrary scripts.

Refactor the code so that we instead expect an arbitrary script to
exist and rename the functionality to "one-time-script". Adapt callers
to use shell utilities instead of Perl so that we can drop the
PERL_TEST_HELPERS prerequisite.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-httpd/apply-one-time-script.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+
+# If "one-time-script" exists in $HTTPD_ROOT_PATH, run the script on the HTTP
+# response. If the response was modified as a result, delete "one-time-script"
+# so that subsequent HTTP responses are no longer modified.
+#
+# This can be used to simulate the effects of the repository changing in
+# between HTTP request-response pairs.
+if test -f one-time-script
+then
+	LC_ALL=C
+	export LC_ALL
+
+	"$GIT_EXEC_PATH/git-http-backend" >out
+	./one-time-script out >out_modified
+
+	if cmp -s out out_modified
+	then
+		cat out
+	else
+		cat out_modified
+		rm one-time-script
+	fi
+else
+	"$GIT_EXEC_PATH/git-http-backend"
+fi