Can't install into a custom prefix

[Michał Sawicz]

It's impossible to install into a custom prefix, files are being installed in absolute paths:

CMake Error at src/cmake_install.cmake:56 (FILE):
  file INSTALL cannot copy file
  "/home/michal/dev/canonical/unity8/unity-notifications/build/src/libnotifyplugin.so.1.0.0"
  to
  "/usr/lib/x86_64-linux-gnu/unity8/qml/Unity/Notifications/libnotifyplugin.so.1.0.0".
Call Stack (most recent call first):
  cmake_install.cmake:38 (INCLUDE)

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: qtdeclarative5-unity-notifications-plugin 0.1.1+14.10.20140602-0ubuntu1
ProcVersionSignature: Ubuntu 3.15.0-5.10-generic 3.15.0-rc8
Uname: Linux 3.15.0-5-generic x86_64
NonfreeKernelModules: wl nvidia
ApportVersion: 2.14.3-0ubuntu1
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Jun 6 09:51:10 2014
SourcePackage: unity-notifications
UpgradeStatus: No upgrade log present (probably fresh install)