debuging...
services_discovery: add SD_CMD_BROWSE
lib: change libvlc_media_discoverer_t creation

libvlc_media_discoverer_new_from_name was creating a services_discovery_t and
was starting it, so libvlc_MediaDiscovererStarted event (or any other events)
could not be received.

To fix that, Split libvlc_media_discoverer_new_from_name into
libvlc_media_discoverer_new and libvlc_media_discoverer_start. That way, we can
attach events between create and start.

libvlc_media_discoverer_new_from_name is now deprecated, but it still works
like before.
libvlc: add libvlc_media_discoverer_browse

Discover media on a specified uri.
lib: add libvlc_MediaDiscovererItemAdded...
dsm: refactor

Move browser.c to common.c. This new file contains common browsing functions
that can be used from an access_t or from a services_discovery_t.
dsm: only one function to browse share and directory
dsm: add "smb://" if not present
dsm/sd: netbios_ns_discover needs a timeout
dsm/sd: discover in a separate thread
dsm/sd: thread stay alive and handle commands
dsm: use libdsm public headers