Trival: ___KEY_OBJ -> ___KEYOBJ in lib/mem.c

___KEY_OBJ was renamed to ___KEYOBJ a little while back, but mem.c
hasn't been updated.

Clean boostrap fails to compile as a result:                                    
                                                                                
mem.c: In function 'print_object':                                              
mem.c:1609:23: error: '___KEY_OBJ' undeclared (first use in this function)      
mem.c:1609:23: note: each undeclared identifier is reported only once for each \
function it appears in                                                          
make[1]: *** [mem.o] Error 1