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

[Роман Кирилич]

Different packages use different style to output some info for user.
They use echo, but prefixes information with different chars ("  >>>
", " ==> ", " >> "  etc.).
I think it will be better if there will be message() function that can
be used for such purpose.
This will not only make all such info messages the same style,
but also this will allow to cache such messages and display them after
upgrade process
(this is very useful when upgrading many packages).
What do you think?