Add a mutex, to protect the double access to cwin->cstate->curr_mobj.
The idea is prevent that change curr_mobj or their tags while anoter thread try to use it.
TODO:
* Use g_object_get(), to get a copy of tags where necessary. Example on __update_current_song_info(), the mutex is almost useless!.
* update_album_art() need a lock, but is slowwww!.
* if(omobj == cwin->cstate->curr_mobj) ?????? How lock it?

p.s: It seems a bit exaggerated, but I think it is necessary
D'Oh!. Bad C-n-p..
Fix lock on pragha-lastfm.c.
Note that before only got safely the pointers to data, but then, the information pointed could change!
Fix lock on pragha-backend.c.
Fix lock on panel.c
Nasty D'Oh!. on prev commit.
Fix lock on notify.c
Fix mpris.c lock
Cri cri.. Without words!.
Fix lock on menu.c
Add pragha_musicobject_dup(), to get a temp Musicobject  and not need to block the entire tag edit dialog.
Fix gui.c lock. 
Fix lock  of  cwin->cstate->curr_mobj on glyr-related.c 
Everything seems fine. But there must be something wrong!.  haha
Add another mutex to control cwin->clastfm->nmobj.
Fix lock on mpris_Player_SetPosition(), although it's a ugly hack.
Compare files of clastfm->nmobj and cstate->curr_mobj before show the button of corrections.
Also, stop clean clastfm->nmobj. Is not necessary.
Ref and save reference in single line.
pragha_playlist_update_current_track() not need mutex.
Use directly g_object_get() to dup property.
Merge branch 'ThreadSafe'

Conflicts:
	src/menu.c
	src/pragha-lastfm.c