Merge branch 'jc/cutoff-config'

"[gc] rerereResolved = 5.days" used to be invalid, as the variable is defined to take an integer counting the number of days. It now is allowed. * jc/cutoff-config: rerere: allow approxidate in gc.rerereResolved/gc.rerereUnresolved rerere: represent time duration in timestamp_t internally t4200: parameterize "rerere gc" custom expiry test t4200: gather "rerere gc" together t4200: make "rerere gc" test more robust t4200: give us a clean slate after "rerere gc" tests