vi: make status line less confusing when we open non-readable files,

vi: make status line less confusing when we open non-readable files,
require rood to use w! when saving non-writable files.
Patch by Natanael Copa <natanael.copa@gmail.com>

update_ro_status                                       -      73     +73
edit_file                                            819     822      +3
colon                                               3440    3425     -15
.rodata                                           128090  128058     -32
file_insert                                          288     235     -53
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/3 up/down: 76/-100)           Total: -24 bytes
   text    data     bss     dec     hex filename
 673344    2740   13968  690052   a8784 busybox_old
 673320    2740   13968  690028   a876c busybox_unstripped