fsfs's fs_serialized_init() not thread safe?

[Blair Zajac]

Wanted to confirm a reading of fs_serialized_init() in libsvn_fs_fs/fs.c in a 
persistent, multithreaded server.

It appears that if fs_serialized_init() is called at the same time by two or 
more threads, then you would have a race on apr_pool_userdata_get() and 
apr_pool_userdata_set().

It looks like a good fix for this would be to have svn_fs_initialize() call down 
into the fs implementation library to set this up?  Would that be a good 
solution to this?  It would need to call into all fs implementation libraries 
though, loading a .so that may never be used.

Blair