HTTP Servers: tame garbage collection
Full garbage collection at each request is too harsh, Mercurial 6.0 provides a setting to calm it down, avoiding to collect the older generation at each request.
Heptapod inner Mercurial servers (HTTP and HGitaly) should honour the setting with a nice default.
More information on https://phab.mercurial-scm.org/D11204 and https://bz.mercurial-scm.org/show_bug.cgi?id=6075