SBS_HOME environment variable must not be wrong when building with sbs

If I have "my own" Raptor installed, chances are tahth I have a SBS_HOME environment variable set which points to my own Raptor.
That leads to a couple of build errors, for example:

'python.exe' is not recognized as an internal or external command, operable program or batch file.
C:\QtSDK\Symbian\SDKs\Symbian3Qt471\epoc32\tools\make.exe: *** [debug-gcce] Error 9009
The process "C:\QtSDK\Symbian\SDKs\Symbian3Qt471\epoc32\tools\make.exe" exited with code 2.
Error while building project untitled37 (target: Symbian Device)
When executing build step 'Make'

Solution: either clear or better correctly set the SBS_HOME environment variable when building with sbs.