Max_cell: 1 sometimes lead to bad results

[mick]

Adding a failing test case here

Given the LLRect

and the options {min:1, max:30, max_cells:1}

I get back 2 cells, both are much larger then the need to be to cover the area. level 0 and 4.

In s2map the same options result in 1 cell at level 8

cc: @tmcw

[mick]

It is for sure related to using S2LatLngRect, If I use a polygon, which is the only thing that s2map uses. I get the cover i expect. Add a test case that works with polygons