Merge branch 'ks/rfc2047-one-char-at-a-time' into maint

When "format-patch" quoted a non-ascii strings on the header files,
it incorrectly applied rfc2047 and chopped a single character in the
middle of it.

* ks/rfc2047-one-char-at-a-time:
format-patch: RFC 2047 says multi-octet character may not be split

diff --cc pretty.c
Simple merge

diff --cc t/t4014-format-patch.sh
Simple merge

diff --cc utf8.c
Simple merge

diff --cc utf8.h
Simple merge