Fix issue #425.

Do not allow a TMS imagery provider's extent to be outside the extent
alowed by the tiling scheme, no matter what the tilemapresource.xml file
says.
Merge pull request #430 from AnalyticalGraphicsInc/issue425

Fix issue #425.
Add a test for issue #425.

Also extended `loadXML` to support testing in the same way that `jsonp` and
`loadImage` do.
Fix broken doc build, and add a comment to loadXML.
Merge pull request #432 from AnalyticalGraphicsInc/issue425

Add a test for issue #425.
Merge remote-tracking branch 'origin/master' into terrain