The httpd-supplied write callback is the leak culprit under Perl
5.16.3. undef-ing it immediately after use keeps a repeated
"git fetch" loop from monotonically increasing memory and FD use
on the Perl shipped with RHEL/CentOS 7.x.
Other endpoints tested showed no increase in memory use under
constant load with "ab -HAccept-Encoding:gzip -k", including the
async psgi_qx code path used by $INBOX_URL/$OBJECT_ID/s/ via
SolverGit module.