enhance error message for missing source files
enhance error message for missing source files

Now prints file name where the source file is referenced.

Change-Id: Ib5d82a51d308ad3b92aada385ba6183174bb20ab
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@nokia.com>

Distrotech/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs,gatzka/qt-labs-qbs,qtproject/qt-labs-qbs,villytiger/qbs,villytiger/qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs,villytiger/qbs,qtproject/qt-labs-qbs,villytiger/qbs,villytiger/qbs,qtproject/qt-labs-qbs,villytiger/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,Distrotech/qbs,qt-labs/qbs,qt-labs/qbs,gatzka/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,Distrotech/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,Distrotech/qbs,gatzka/qt-labs-qbs,Distrotech/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,qt-labs/qbs