Merge lp://staging/~gordallott/unity/fix-dash-icon-aspect-ratio into lp://staging/unity

Few notes:
- I think "cairo_scale (cr, 1.0f, 1.0f);" does nothing, unless you added it to highlight you're not scaling the context, but in this case it might be better to add a simple comment and removes redundant calls.
- if you use "CAIRO_OPERATOR_CLEAR" then the call "cairo_set_source_rgba(cr, 1.0, 1.0, 1.0, 0.0);" is useless, you can remove it (or use it with "CAIRO_OPERATOR_SOURCE" instead).
- you calculate translation with "(width - (pixbuf_width * scale)) * 0.5, (height - (pixbuf_height * scale)) * 0.5)", but this can handle in float numbers, while I think we want integers to avoid misalignment to the cairo grid: simply cast them to be integers "(int)((width - (pixbuf_width * scale)) * 0.5), (int)((height - (pixbuf_height * scale)) * 0.5))", and then check again if it's correctly aligned.

A part from the quick overview on the cairo code, I didn't test the real math to see if works correctly, but I trust gord as it seems pretty simple math ;)

Good practice (not to apply to this code, as I think context are deleted after the functions close):
When modifying either the cairo matrix (calls to "cairo_scale" or "cairo_translate") or operators I'd use "cairo_save(cr);" then "cairo_restore(cr);" afterwords, because if the cairo context lives after your drawing and other drawing methods use it, they might continue from the previous state you're modified, leading to weird behaviors.

looks good, thx gord!