WHEN STDIN IS A PIPE
            
Problem: Mysqlbinlog does not accept the input from STDIN when 
STDIN is a pipe. This prevents the users from passing the input file
through a shell pipe.    

Background: The my_seek() function does not check if the file descriptor
passed to it is regular (seekable) file. The check_header() function in
mysqlbinlog calls the my_b_seek() unconditionally and it fails when
the underlying file is a PIPE.  
            
Resolution: We resolve this problem by checking if the underlying file
is a regular file by using my_fstat() before calling my_b_seek(). 
If the underlying file is not seekable we skip the call to my_b_seek()
in check_header().

client/mysqlbinlog.cc:
  Added a check to avoid the my_b_seek() call if the
  underlying file is a PIPE.