Problem:
=======
The return value from my_b_write is ignored by: `my_b_write_quoted',
`my_b_write_bit',`Query_log_event::print_query_header'

Most callers of `my_b_printf' ignore the return value. `log_event.cc' 
has many calls to it. 

Analysis:
========
`my_b_write' is used to write data into a file. If the write fails it
sets appropriate error number and error message through my_error()
function call and sets the IO_CACHE::error == -1.
`my_b_printf' function is also used to write data into a file, it
internally invokes my_b_write to do the write operation. Upon
success it returns number of characters written to file and on error
it returns -1 and sets the error through my_error() and also sets
IO_CACHE::error == -1.  Most of the event specific print functions
for example `Create_file_log_event::print', `Execute_load_log_event::print'
etc are the ones which make several calls to the above two functions and
they do not check for the return value after the 'print' call. All the above 
mentioned abuse cases deal with the client side.

Fix:
===
As part of bug fix a check for IO_CACHE::error == -1 has been added at 
a very high level after the call to the 'print' function.  There are 
few more places where the return value of "my_b_write" is ignored
those are mentioned below.

+++ mysys/mf_iocache2.c    2012-06-04 07:03:15 +0000
@@ -430,7 +430,8 @@
           memset(buffz, '0', minimum_width - length2);
         else
           memset(buffz, ' ', minimum_width - length2);
-        my_b_write(info, buffz, minimum_width - length2);

+++ sql/log.cc	2012-06-08 09:04:46 +0000
@@ -2388,7 +2388,12 @@
     {
       end= strxmov(buff, "# administrator command: ", NullS);
       buff_len= (ulong) (end - buff);
-      my_b_write(&log_file, (uchar*) buff, buff_len);

At these places appropriate return value handlers have been added.