bug#19603: 24.4.51; Improve emacs startup message.

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

> Now emacs packages are widely used,
> it would be great to improve the startup message of emacs with a link
> about how to quickly setup package.el to be usable.
> I have regularly people complaining "It is not working" because
> they install packages through package.el and they don't add in their
> init file `package-initialize',

Right, we do call package-initialize automatically for them, but we do
it "too late" in many cases.  Maybe the best option is to emit some
message at startup in the following case:
- there are packages installed.
- the .emacs file is non-empty.
- there is no call to package-initialize in the .emacs file.

> or they try compiling autoload file etc...

No idea how/why they'd do that, hence no idea how to help them
understand they shouldn't/needn't do it.  This said, it should do no
harm, does it?


        Stefan