Send filter expression string to session daemon

Send the filter expression string along with the filter's bytecode
to the session daemon. The session daemon now stores the filter
expression. This makes it possible to list the filter's expression
when listing events.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Add a dependency to libxml2

libxml2 2.7.6 is the oldest supported version.
This is the version distributed as part of RHEL 6.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Add a config_writer API based on libxml2

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Add session configuration XSD

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
session_find_by_name does not need a non-const name parameter

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Add a save API to lttng-ctl

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Session configuration save feature added to session daemon

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Add a save command based on the save API to the lttng client

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>