Merge branch 'aw/gc-lockfile-fscanf-fix' into maint

"git gc" tries to avoid running two instances at the same time by reading and writing pid/host from and to a lock file; it used to use an incorrect fscanf() format when reading, which has been corrected. * aw/gc-lockfile-fscanf-fix: gc: call fscanf() with %<len>s, not %<len>c, when reading hostname