remote-helpers: build in platform independent directory

The build directory which is used by distutils depends on the platform
(e.g. build/lib on Fedora 13, build/lib.linux-i686-2.6 on Ubuntu 9.04).
But test-lib.sh expects to find the build in build/lib which can cause
t5800-remote-helpers.sh to fail early.

Override distutils' choice so that the build is always in build/lib.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git_remote_helpers/setup.cfg

@@ -0,0 +1,3 @@
+[build]
+build_purelib = build/lib
+build_platlib = build/lib