tests: locate i18n lib&data correctly under --valgrind
The new t020[01] for gettext support did not find git-sh-i18n and the
translation data when run under --valgrind: lib-gettext.sh tried to
locate them under $GIT_EXEC_PATH, which normally is the git build
directory, but is changed by --valgrind to point to the wrappers.
Introduce a new variable $GIT_BUILD_DIR which can be used to locate
data that resides under the build directory, and use that instead.
Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>