Update to the modules system. Fixed:

Update to the modules system. Fixed:
 - get rid of smb_probe_module
 - merge older updates from 3.0
 - introduced register_subsystem() and register_backend() functions
 - adapt ntvfs and charset to use new register functions
 - made smb_load_modules() work recursively (e.g. 'preload modules = /usr/lib/samba')
 - got rid of some old remains

Things that still need work:
 - Did I break tankFS? I don't think so, but I can't test it here :-(
 - Add 'postload modules = ' (for modules that need to be loaded after fork() in smbd, if applicable)
 - Convert RPC, auth, passdb, etc to use new register_{subsystem,backend}() functions
 - Accept wildcards in 'preload modules' option, instead of loading recursively
(This used to be commit 3433c4c71f20dde96d30e02a49bbe09a9ce6c036)