testcase.py: raise instead of assert_(false) in compareImage to get a better error message.
testcase.py: raise instead of assert_(false) in compareImage to get a better error message.

svn path=/trunk/libavg/; revision=3390

yyd01245/libavg,scotty007/libavg,scotty007/libavg,th3infinity/libavg,libavg/libavg,libavg/libavg,th3infinity/libavg,th3infinity/libavg,hoodie/libavg,yyd01245/libavg,libavg/libavg,hoodie/libavg,hoodie/libavg,yyd01245/libavg,hoodie/libavg,scotty007/libavg,yyd01245/libavg,scotty007/libavg,libavg/libavg,th3infinity/libavg