Creates a wrapper for Maps Unit tests to make it easier to swap out maps keys

Updated this patch and moved it to gwt-code-reviews, see:

http://gwt-code-reviews.appspot.com/369803

[zundel]

I'm looking for a brave soul to review this one.

-Eric.

http://galgwt-reviews.appspot.com/53602/diff/1/12
File maps/src/com/google/gwt/maps/client/MapPaneType.java (right):

http://galgwt-reviews.appspot.com/53602/diff/1/12#newcode59
Line 59: OVERLAY_LAYER_PANE("$wnd.G_MAP_OVERLAY_LAYER_PANE");
unrelated to other changes, this updates the API with a new pane value.

http://galgwt-reviews.appspot.com/53602/diff/1/2
File maps/test/com/google/gwt/maps/client/MapPaneTypeTest.java (right):

http://galgwt-reviews.appspot.com/53602/diff/1/2#newcode37
Line 37: }
unrelated to the test framework changes in particular, this is an entirely new
test (but written in the new style)

http://galgwt-reviews.appspot.com/53602/diff/1/10
File maps/test/com/google/gwt/maps/client/MapUIOptionsTest.java (left):

http://galgwt-reviews.appspot.com/53602/diff/1/10#oldcode44
Line 44: RootPanel.get().add(map);
this turns out to be extraneous (only one test)