Makefile.am: Run tests with CK_FORK=no

With this environment variable set, we'll get correct errno values back
if and when a test fails, as Check won't mask them with its own.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
client: Add a riemann_client_send_message_oneshot() function

This function does the same as riemann_client_send_message(), except
that it will always free the message once it is sent. This can be used
to send in-place constructed messages that will not be reused.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
src/: Convert the demos to riemann_client_send_message_oneshot()

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>