xbmc: update to xbmc-13.alpha-0efa87e

Signed-off-by: Stephan Raue <stephan@openelec.tv>
Merge branch 'master' of github.com:OpenELEC/OpenELEC.tv
installer: rework buildscript

Signed-off-by: Stephan Raue <stephan@openelec.tv>