Fix: Define __STDC_LIMIT_MACROS to fix C++ builds

Necessary to include the fixed-width type limits on glibc versions
older than 2.18 when building with a C++ compiler.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: kernel channel destroy on consumer if sent

An enable-channel immediately followed by a destroy session triggered an
assert on the consumer followed by the shutdown of the consumer thread
for the kernel.

This fix make sure we don't ask the consumer to destroy a channel if not
previously sent to it and handle not found channel on destroy.

Fixes #643

Signed-off-by: David Goulet <dgoulet@efficios.com>

Conflicts:
	src/common/kernel-consumer/kernel-consumer.c
	- No health in stable-2.3 thus had to remove a health update
	code statement.