Merge branch 'jk/utf-8-can-be-spelled-differently' into maint

Some platforms and users spell UTF-8 differently; retry with the
most official "UTF-8" when the system does not understand the
user-supplied encoding name that are the common alternative
spellings of UTF-8.

* jk/utf-8-can-be-spelled-differently:
  utf8: accept alternate spellings of UTF-8

diff --cc utf8.c
Simple merge