Make all tests pass again.

This includes three fixes:

* Round when compairing center coordinates (`panel.PrintMap` test)
* call `panel.PrintMap.bind` in `afterlayout` event
* Do not destroy `map` which is already destroyed when tearing down
  tests (`data.LayerStore` test)

The tests now all pass in Chrome 21 and Firefox 20 (both on a linux box)
and also in Internet Explorer 8 (Windows XP).
Merge pull request #176 from marcjansen/test-fixes

Make all tests pass again.