This updates assertQueries() to check for and compare subquery

information. This takes in an inner_query attribute that matches the

query comparison dictionary and checks against it.
This wasn't supported before, and because of that, this support must be

optional or we'll break existing tests. Currently, consumers can pass in

check_subqueries=True to enable this. That will be the default in

Djblets 5. For now, if a subquery is found and no explicit

check_subqueries value is provided, a deprecation warning will be

emitted.
Formatting has also improved, in part to help output subquery comparison

details. All values are now passed through pprint.pformat(), and if

the results span multiple lines, it will be formatted with proper

indentation and alignment to help with reading the output.

All Djblets and Review Board unit tests pass.