set callbacks just before fetch, clear them after (fixes #403).
Add some tests for refcounts to check for leaks
Hard-code callback version because we'll need to change the defs if it changes.
Don't test refcounts in pypy as they don't make sense there
Fix use of skipIf.
Ensure self handle stays alive - keeping it in callbacks is not enough.
Merge remote-tracking branch 'mduggan/remote-refcount-fix'