mediastreamer: add missing host-gettext dependencies and other fixes

Fixes:
http://autobuild.buildroot.org/results/5e6c465c56f85a3017900613facc6e54c85d32da/build-end.log

.

While we're at it, add the usual comment header block at the beginning
of the file, as well as licensing informations.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>