[pacman-dev] add message() function call for use in *.install/.PKGINFO files

[Роман Кирилич]

> the whole "echo in post_install" custom should be avoided. think of any
> gui - their stdout is even invisible in most cases
>
> it's up to the Arch devs how they solve this problem - in Frugalware we
> use to add README.Frugalware files for packages and such infos are
> described there. probably such READMEs are not preferred by them since
> by default they remove all the docs from the packages

README can be good if it will be displayed automatically after package install.
This is a job of any libalpm front-end anyway.
It should be treated like .PKGINFO or .FILELIST files - I mean these
README files should be used for front-end work only, and not installed
anywhere.
There is another thing - some packages generates some progress info
during install (like ">>> Genreating initial ramdisk... done").
- this should be addressed too, maybe with something like
status_message() function, or something else.
By addressing this issues now we can avoid different custom "echo in
post_install" things for different packages in different front-ends.
I don't know much about libalpm/pacman3 internals yet, but I think
that these issues can be addressed.