In preparation for moving `git serve` into `test-tool` (because it
really is only used by the test suite), we teach the `test-tool` the
useful trick to change the working directory before running the test
command, which will avoid introducing subshells in the test code.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>