Use self_and_ancestors in page_active? helper

[mamhoff]

This helper used a method that has been removed in #1813.
I'm also adding some specs.

[hound]

Some files could not be reviewed due to errors:

Error: unrecognized cop Lint/DuplicateBranch found in .rubocop.yml, unrecogni...

Error: unrecognized cop Lint/DuplicateBranch found in .rubocop.yml, unrecognized cop Lint/DuplicateRegexpCharacterClassElement found in .rubocop.yml, unrecognized cop Lint/EmptyBlock found in .rubocop.yml, unrecognized cop Lint/EmptyClass found in .rubocop.yml, unrecognized cop Lint/NoReturnInBeginEndBlocks found in .rubocop.yml, unrecognized cop Lint/ToEnumArguments found in .rubocop.yml, unrecognized cop Lint/UnexpectedBlockArity found in .rubocop.yml, unrecognized cop Lint/UnmodifiedReduceAccumulator found in .rubocop.yml, unrecognized cop Style/ArgumentsForwarding found in .rubocop.yml, unrecognized cop Style/CollectionCompact found in .rubocop.yml, unrecognized cop Style/DocumentDynamicEvalDefinition found in .rubocop.yml, unrecognized cop Style/NegatedIfElseCondition found in .rubocop.yml, unrecognized cop Style/NilLambda found in .rubocop.yml, unrecognized cop Style/RedundantArgument found in .rubocop.yml, unrecognized cop Style/SwapValues found in .rubocop.yml

[tvdeyen]

Thanks