Major audio format handler cleanups.

Major audio format handler cleanups.

The main change is the replacement of afhi->taginfo by more specific
fields: This patch adds struct taginfo to the audio format handler
info struct.

The prefix is no longer stored inside the osl database, i.e. it is
no longer duplicated for each audio file.

The tag information is only stored in memory as a dynamically allocated
string if it is new, i.e. if the struct was generated by the audio format
handler. If it was retrieved from the database, pointers to the memory
mapped table are used instead.

The crappy fixup_info_string() function is gone. It was too ugly to live.
Of course, this re-introduces the bug it fixed, but as we broke the
on disk format with this patch anyway, we might as well fix it right(TM).
This will be done in a subsequent patch.

afhi->eof_tv is gone as well. It was not useful at all.