Merge branch 'en/batch-prefetch' into seen

In a lazy clone, "git cherry" and "git grep" often fetch necessary
blob objects one by one from promisor remotes.  It has been corrected
to collect necessary object names and fetch them in bulk to gain
reasonable performance.

* en/batch-prefetch:
  grep: prefetch necessary blobs
  builtin/log: prefetch necessary blobs for `git cherry`
  patch-ids.h: add missing trailing parenthesis in documentation comment

diff --cc builtin/grep.c
Simple merge

diff --cc t/t7810-grep.sh
Simple merge