Comint, term, and compile now set EMACS

Comint, term, and compile now set EMACS

This fixes directory tracking in ansi-term, at the expense of
breaking some usages of 'configure'.  Setting EMACS is meant to be
a somewhat temporary measure, until Bash 4.4 comes out and is
common.  (Bug#20484).
* etc/NEWS: Document this.
* lisp/comint.el (comint-exec-1):
* lisp/net/tramp-sh.el (tramp-remote-process-environment):
* lisp/progmodes/compile.el (compilation-start):
* lisp/term.el (term-exec-1):
Go back to setting the EMACS environment variable, for backward
compatibility to Bash 4.3 and earlier.