Strict verification of resource deletion in TemporaryFolder rule

PR that adds support of strict verification of deleted resources when using `TemporaryFolder` rule #1001
I'm not sure having the test delete the folder should cause `TemporaryFolder` to complain that it can't delete the file when `strictlyVerifyDeletions()` was called. The indention of "strictlyVerifyDeletions" is to ensure that the files are deleted when the test is complete, and deleting it manually meets that need.

You might need to have the test subclass `TemporaryFolder` to simulate the `delete()` call not deleting the files