Arch Linux

Description:
Installing the already downloaded packages of today's KDE update took almost half an hour again due to gtk-update-icon-cache being executed after upgrading every single package that contains an icon. However, as far as I understand, it would only be necessary to do this once at the end of the install process in order to speed it up by a lot, and since icon cache updates are not critical to system stability, it should be safe to put it there.

My implementation proposal would be the following:
- For every hook for which it makes sense, add another "_once" hook, for instance "post_install_once()".
- Buffer every command inside those hooks, ignoring commands with the same command line aleady in the buffer
- Flush the command buffer after every processing stage (removing, upgrading, ..)

Additional info:
* package version(s): All
* config and/or log files etc.

Steps to reproduce:
Update all KDE packages, for instance