Doc fix for lexical-binding being in line one.

Doc fix for lexical-binding being in line one.

Ref http://lists.gnu.org/archive/html/emacs-devel/2012-01/msg00543.html

* doc/lispref/variables.texi (Using Lexical Binding):
Mention that lexical-binding should be set in the first line.

* src/lread.c (syms_of_lread): Doc fix.

* lisp/emacs-lisp/tabulated-list.el, lisp/progmodes/f90.el:
Move lexical-binding file-local to line one.

* etc/NEWS: lexical-binding should be ine the first line.