t0051: test GIT_TRACE to a windows named pipe

Create a test-tool helper to create the server side of
a windows named pipe, wait for a client connection, and
copy data written to the pipe to stdout.

Create t0051 test to route GIT_TRACE output of a command
to a named pipe using the above test-tool helper.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>