vi: multiple fixes by Natanael Copa <natanael.copa@gmail.com>

* the puzzling message on error is replaced with strerror(errno)
  so it should be even more detailed and smaller at the same time.
* merged code in edit_file() and code for ':edit <file>' in colon() into
  new func init_text_buffer(). Was horribly duplicate. Moved most of
  error/sanity checking to file_insert(). Result is that you get a proper
  validation (prevent reading /dev/*) and error messages for ':r <file>' 
* renamed 'cfn' to 'current_filename' for improved readability
* merged smallint vi_readonly and readonly into bitfields into
  readonly_mode to save space.
* added text_size variable to keep track how big the text buffer is.
  This is used to fix a buffer overflow. To reproduce bug:
  ./busybox vi TODO
  :r Makefile
  vi segfaults due to no buffer checking is done at all. som redesign is
  needed here but i added a check in text_hole_make() to aviod the
  segfault at least.
* removed isblnk() and use isblank(3) instead.
* fixed compiler warning by displaying the return code for :!<command>
  This makes things bigger than needed but since the patch reduces the
  overall size... (see below)
* new func next_tabstop(int) merges some duplicate code. There are more
  cuplicode here but i couldnt find a good way to merge them.
* Fix *ANNOYING* placement of cursor on '\t' characters. To reproduce:
    echo -e "\thello" > file1
    ./busybox vi file1
  Try to insert some text at the beginning of line. Text will be inserted
  but cursor is blinking somewhere else. The patch should make busybox vi
  behave more like original vi(m). Costs a few bytes but its worth it
  imho.
* new_text() is moved into init_text_buffer()
* the previously added update_ro_status() was moved info file_insert due
  to duplication removal mentioned above.
function                                             old     new   delta
init_text_buffer                                       -     245    +245
file_insert                                          312     420    +108
next_tabstop                                           -      82     +82
text_hole_make                                       154     171     +17
do_cmd                                              5093    5100      +7
static.cmd_mode_indicator                              -       5      +5
refresh                                             1248    1253      +5
current_filename                                       -       4      +4
yank_delete                                          161     164      +3
what_reg                                              96      99      +3
end_cmd_q                                             78      81      +3
char_insert                                          440     442      +2
readonly_mode                                          -       1      +1
vi_readonly                                            1       -      -1
setops                                               154     153      -1
readonly                                               1       -      -1
vi_setops                                              4       1      -3
string_insert                                        161     158      -3
cfn                                                    4       -      -4
show_status_line                                     532     514     -18
readit                                               519     500     -19
move_to_col                                          161     138     -23
vi_main                                              495     433     -62
isblnk                                                75       -     -75
.rodata                                             4751    4655     -96
edit_file                                            892     787    -105
new_text                                             125       -    -125
update_ro_status                                     131       -    -131
colon                                               3848    3667    -181
------------------------------------------------------------------------------
(add/remove: 5/6 grow/shrink: 8/10 up/down: 485/-848)        Total: -363
bytes
   text    data     bss     dec     hex filename
  34751     873    4260   39884    9bcc busybox_old
  34439     877    4260   39576    9a98 busybox_unstripped

0 files changed, 0 insertions, 0 deletions