The electric behavior of sh-electric-here-document-mode (activated by
default) is annoying when someone does not want to insert a
here-document. For example, the here-string syntax requires to insert
<<<, but the second insertion will trigger the here-document.

Steps taken:
- activate `shell-script-mode`
- enter the following text:

       read line <<< "Line of text"

Expected result: the buffer contains

       read line <<< "Line of text"

Actual result: the buffer contains

       read line <<EOF
       < "Line of text"
       EOF

This report follows from this discussion:
http://thread.gmane.org/gmane.emacs.devel/183318

Solutions are also discussed there, for example tweaking the trigger so
that you need more than just '< <' to insert the here-doc.