Add test case from #216.
Add test case from #216.

The error exposed by this test case no longer happens after the
coalescer was rewritten to to follow the Budimlic paper. It's still a
good coalescer test.

Fixes #216 by including the test case.

sunfishcode/cretonne,sunfishcode/cretonne,stoklund/cretonne,stoklund/cretonne,stoklund/cretonne,sunfishcode/cretonne