Merge branch 'dd/sequencer-utf8'

Merge branch 'dd/sequencer-utf8'

Handling of commit objects that use non UTF-8 encoding during
"rebase -i" has been improved.

* dd/sequencer-utf8:
  sequencer: reencode commit message for am/rebase --show-current-patch
  sequencer: reencode old merge-commit message
  sequencer: reencode squashing commit's message
  sequencer: reencode revert/cherry-pick's todo list
  sequencer: reencode to utf-8 before arrange rebase's todo list
  t3900: demonstrate git-rebase problem with multi encoding
  configure.ac: define ICONV_OMITS_BOM if necessary
  t0028: eliminate non-standard usage of printf