[cairo] cairo_text_extents() wrong on win32 for transformed context

[T Rowley]

I've been having a problem with cairo_text_extents on win32 (cairo 
0.5.0).  With a translated context it returns the correct results, but 
with on a context with a rotation or skew matrix set, the resulting box 
has some transformation I haven't been able to discern.  The same code 
works fine on linux and the boxes are as expected.