Merge branch 'maint-1.6.0' into maint-1.6.1

* maint-1.6.0:
  grep: fix segfault when "git grep '('" is given
  Documentation: fix a grammatical error in api-builtin.txt
  builtin-merge: fix a typo in an error message

diff --cc builtin-merge.c
Simple merge

diff --cc grep.c
Simple merge

diff --cc t/t7002-grep.sh
Simple merge