already existed but was only used by modules as far as is know). This
is done in the module_Need function. Needed module names now have this
syntax: '<module>[@<name>]'. If the @<name> part is present, once the
needed module is found it will change p_this->psz_object_name to <name>.
In about 99% of the module_Need calls, p_this is the module's parent
object so this is ok. The remaining calls won't use this syntax so it's
ok i guess :)

* Add new vlc_object_find_name function. It works like vlc_object_find
but uses a string (name) instead of an integer (type) as its second
argument.

* Change the marq, mosaic and logo commands in rc.c. They now take the
target object's name as first argument. Example:

Launch vlc with:
./vlc -I rc --no-audio --sub-filter "marq@test{marquee=Hello}:marq@testouille{marquee=Test}" ~/media/redefined-nintendo.mpg

Then issue the following command to move the second marq:
marq-x testouille 100

(and while testing I fixed #745)