misc/emacs: Greatly improve go-mode for Emacs.
The original go-mode is plagued with odd behaviour, lack of
behaviour typical to modes in Emacs and bugs.
This change rewrites great parts of go-mode (basically only
keeping the gofmt and godoc functions).
Additionally it adds new features such as manipulating package
imports.
For more information please see
https://groups.google.com/group/golang-nuts/browse_frm/thread/
3a9d6dae3369c0b5/
1efe65e2f7afb190
Fixes #3618.
Fixes #4240.
Fixes #4322.
Fixes #4671.
Fixes #4726.
R=golang-dev, fullung, sameer, cw, arthur, proppy, adonovan, rsc, bradfitz
CC=golang-dev
https://golang.org/cl/
7314113