Merge branch 'jc/custom-comment-char'

Allow a configuration variable core.commentchar to customize the
character used to comment out the hint lines in the edited text from
the default '#'.

* jc/custom-comment-char:
  Allow custom "comment char"

diff --cc Documentation/config.txt
Simple merge

diff --cc builtin/branch.c
Simple merge

diff --cc builtin/commit.c
Simple merge

diff --cc builtin/fmt-merge-msg.c
Simple merge

diff --cc builtin/merge.c
Simple merge

diff --cc cache.h
Simple merge

diff --cc config.c
Simple merge

diff --cc environment.c
Simple merge

diff --cc t/t7502-commit.sh
Simple merge

diff --cc wt-status.c
Simple merge