byte-compiler emacs-18 compatibility mode should be removed

[Miles Bader]

I've been (slowly) working on the byte-compiler support for lexical
binding, and the compatibility code intended to allow the compiler to
emit emacs-18 compatible output has proven to be a real annoyance.

I'm obviously not going to bother trying to support emacs-18 for the new
additions, but also I think it would be an improvement to simply remove
the emacs-18 compatibility stuff altogether.  It only serves to add
unnecessary complexity to the compiler, and I think the 3 remaining
emacs-18 users in the world probably already have a byte-compiler that
works for them...

Objections?

-Miles
-- 
Yo mama's so fat when she gets on an elevator it HAS to go down.