I did a global search in the codebase and found hundreds of cases of Piwik_XYZ written in the codebase, mostly in comments, such as Piwik_Auth, Piwik_Db, Piwik_API, etc.
We should remove these references and replace with correct phpdoc blocks (or simply remove).
This would conclude our effort of migrating the whole codebase from pre-namespace to full namespace support (see also: #4074 )
It's worth reading up on http://www.phpdoc.org/docs/latest/for-users/phpdoc/tags/package.html
I suggest the following:
In dde7c3744b0156ce89a3d1cbe047fa8d880cdbaa: Removing last Piwik_ occurences
In 217b22b3309364edc4231218f52983165dd304e1: Fixes #4609 Removing last mentions of Piwik_ -- Looking sharp now!