bug#3226: here-document syntax inference and completion is broken

[Chong Yidong]

> Cook yourself up a bash script and type a line of code like:
> for i in $(/bin/vim <<
>
> A default emacs install will complete with "EOF\n\nEOF" (in a more
>clever fashion so the rest of the line is undisturbed), and place the
>cursor on the new blank line.  This is incorrect behaviour, as it
>breaks entry of BASH here-strings when the user's intent is still
>ambiguous.  This should only respond to things ending in, for example
>"<< " or possibly "<<E", but certainly NOT just "<<".
>
> Further, emacs does something outright wrong: An attempt to fix the
>situation by inserting another '<' between the "<<" and "EOF" +results
>in ANOTHER pair of "EOF" being inserted in a syntactically invalid way.

I fixed the second problem, but I don't see any easy way to solve the
first one.

(The difficulty of fixing the first bug is illustrative of the problems
with individual major modes rolling their own "electric" completion
facilities.  It might be nice to have a minor mode that provides a
unified framework for this kind of functionality; which may also need
built-in support.)