Merge branch 'ls/checkout-encoding'

The new "checkout-encoding" attribute can ask Git to convert the contents to the specified encoding when checking out to the working tree (and the other way around when checking in). * ls/checkout-encoding: convert: add round trip check based on 'core.checkRoundtripEncoding' convert: add tracing for 'working-tree-encoding' attribute convert: check for detectable errors in UTF encodings convert: add 'working-tree-encoding' attribute utf8: add function to detect a missing UTF-16/32 BOM utf8: add function to detect prohibited UTF-16/32 BOM utf8: teach same_encoding() alternative UTF encoding names strbuf: add a case insensitive starts_with() strbuf: add xstrdup_toupper() strbuf: remove unnecessary NUL assignment in xstrdup_tolower()