QMake fails to build with build directories deeper then the source directory

This is a follow up to QTCREATORBUG-1036

Steps to reproduce:

a) Create a dummy project in (touch main.cpp && qmake -project is good enough)
C:\TMP\dummy\ [1]

b) create a build directory
c:\TMP\dummy-build\desktop [2]

c) Run qmake in that build directory

d) Check the Makefile for the qmake target
It should be -spec ..\..\..\path-to-qt\mkspecs\somespec
That is relative and as many ".." as the build directory is deep
And more ".." than the source directory is deep

e) make qmake
This will call qmake - spec ../../../path-to-qt\mkspecs\somespec

Diving into the qmake code, the current working directory is set to c:\TMP\dummy
And on line 1353 if (QFile::exists( ../../../path-to-qt/mkspecs/somespec + "/qmake.conf")) returns true
which leads to line 1354 Option::mkfile::qmakespec = QFileInfo("C:\TMP\dummy/../../../path-to-qt/mkspecs/somespec/qmake.conf").absoluteFilePath()
which leads to setting Option::mkfile::qmakespec to C:/../path-to-qt/mkspecs/somespec/qmake.conf

And qmake then fails with:
Failure to read QMAKESPEC conf file c:/../path-to-qt/mkspecs/somespec/qmake.conf
MAKEFILE_GENERATOR variable not set as a result of parsing : C:/QtCreator/qtcreator-2.0.0beta/untitled15/untitled15.pro. Possibly qmake was not able to find files included using "include(..)" - enable qmake debugging to investigate more.

[1] This directory needs to be not parent directory of the qt directory and be not deep in the file hierarchy and probably on the same drive as qt
[2] This directory needs to be one level deeper then [1]