The previous fix introduced another leak; as it made
Banzai::Filter::SanitizationFiler#customized? always return false, so we
were always appending two elements to
HTML::Pipeline::SanitizationFilter::WHITELIST[:elements]. This growth in
the elements array would slow the sanitization process over time.
In Banzai::Filter::SanitizationFilter#customize_whitelist, we append
three lambdas that has reference to the SanitizationFilter instance,
which in turn (potentially) has a reference to the following chain:
context hash -> Project instance -> Repository instance -> lookup hash
-> various Rugged instances -> various mmap-ed git pack files.
All of the above is not garbage collected because the array we append
the lambdas to is the constant
HTML::Pipeline::SanitizationFilter::WHITELIST.
Phil Hughes