Make senders independent of afs and osl.

Make senders independent of afs and osl.

Although senders don't know anything about the osl databases of
the audio file selector, all senders currently include afs.h and
osl.h. This is because:

	* senders are part of para_server, so they include server.h,

	* server.h has an audio_file_data structure embedded in struct
	misc_meta_data, so struct audio_file_data must be declared
	before server.h is included,

	* struct audio_file_data is declared in afs.h,

	* afs.h makes use of structures defined in <osl.h>.

This patch moves the declaration of struct audio_file_data from afs.h
to afh.h, which is also included by all senders. This allows to remove
the two include directives for afs.h and osl.h from all three senders.