bug#9800: Incomplete truncated file buffers from the /proc filesystem

[Juri Linkov]

Large files from the /proc filesystem are visited incompletely,
their file buffers are truncated at the position 65536.
One possible test case to reproduce this is to load enough libraries
with e.g. (imagemagick-register-types) and visit Emacs's maps file
in /proc/$PID/maps.

Andreas said in 
http://lists.gnu.org/archive/html/emacs-devel/2011-10/msg00782.html
that it's due to this code in `insert-file-contents':

          /* The file size returned from stat may be zero, but data
             may be readable nonetheless, for example when this is a
             file in the /proc filesystem.  */
          if (end_offset == 0)
            end_offset = READ_BUF_SIZE;

How this could be fixed?  Should it keep reading while more data can be
read from the file?