I tried to install three wiki instances on the same server, using same
extension file resources.
Following the advice at
http://www.mediawiki.org/wiki/Manual:Wiki_family#Scenario_5:_Multiple_wi
kis_sharing_common_resources I declared a new variable
"$wgExtensionPath".
Including extensions this way works very well for most of it.
But for some extensions, I found that they use additional path variables
to their files internally, which refer to "extensions/ExtensionName"
hardcoded.
Of course, this makes it hard to maintain proper inclusion/update of
such extensions, because the internal variables have to be patched.
So it would be nice, if MediaWiki introduces a common "$wgExtensionPath"
variable.
Then extension developers can use this variable as basic extension
directory path and wiki administrators can change it as needed very
easy.
Daniel