title: sed -i not working with x11 alone
body: <pre><code>$ cat my_test.txt  
  My test for sed starts here :)  
  $ sed -i '1s/^/\hi.../' my_test.txt  
  $ cat my_test.txt  
  hi...My test for sed starts here :)  
  $ sed -i '1s/^/\x11/' my_test.txt  
  $ cat my_test.txt  
  hi...My test for sed starts here :)  
  $ sed -i '1s/^/\x11.../' my_test.txt  
  $ cat my_test.txt  
  ...hi...My test for sed starts here :)   
  $ sed -i '1s/^/\x11...x11/' my_test.txt    
  $ cat my_test.txt  
  ...x11...hi...My test for sed starts here :)  
  </code></pre>
  
  <p>Compared  the strace output and here it goes respectively</p>
  
  <pre><code>read(3, "My test for sed starts here :)\n", 32768) = 31  
  write(4, "hi...My test for sed starts here"..., 36) = 36  
  
  read(3, "hi...My test for sed starts here"..., 32768) = 36  
  write(4, "\21hi...My test for sed starts her"..., 37) = 37  
  
  read(3, "\21hi...My test for sed starts her"..., 32768) = 37  
  write(4, "\21...\21hi...My test for sed starts"..., 41) = 41  
  
  read(3, "\21...\21hi...My test for sed starts"..., 32768) = 41  
  write(4, "\21...x11\21...\21hi...My test for sed"..., 48) = 48  
  </code></pre>