install_hook once from multiple plugins

[Alexander Belchenko]

Hi,

I'm pondering on some vague idea when I want to share some functionality 
between 2 (or may be more) plugins. This functionality is based on the 
usage of hooks. So I'm trying to understand what is the right path will 
be for this: extract the required hook into 3rd plugin and make that 3rd 
plugin mandatory for first two, or thinking about implement method in 
bzr like `install_unique_hook` and pass special argument here (some tag) 
to avoid the same hook installed twice.

For example, I've added MRU commit-history list to QBzr and then 
realized I can provide access to this feature for CLI users. So CLI 
users don't need to install QBzr but can use another (lightweight) 
plugin, named, say, commit-history, or mru-history.

On the other hand maybe I should make mru-history dependency for QBzr 
and therefore make MRU functionality optional in QBzr if that 
(imaginary) plugin is not installed? Something similar we do for 
bzr-search... But I'm not sure I want to create mru-history plugin right 
now.

Or maybe I bother about such things too early?

Alexander