Merge lp://qastaging/~gordallott/unity/fix-relayout-cycle-bug into lp://qastaging/unity

fixes a problem with the relayout cycle in unity, so for some reason, since i reinstalled ubuntu standalone-dash wasn't working, a relayout cycle was causing a relayout cycle for infinity. not fun times.

tracked it down to:
content_layout_->SetMinMaxSize(content_geo_.width, content_geo_.height);

in DashView.cpp - content_layout is a child of layout_, so i think what was happening was that the content_layout_ and the layout_ were having a bit of a tizzy and fighting it out in relayout cycles.

setting layout_ to have a minmax size instead seems to work well, but i'm changing code here that might have hidden problems that i don't know about (not doing what the spec says or whatever) so give it a good go first

oh also removed the signals ongeometrychange, because they themselves cause a geometry change and thats scary, so do that in postlayout