Merge branch 'cn/bom-in-gitignore' into maint

Teach the codepaths that read .gitignore and .gitattributes files that these files encoded in UTF-8 may have UTF-8 BOM marker at the beginning; this makes it in line with what we do for configuration files already. * cn/bom-in-gitignore: attr: skip UTF8 BOM at the beginning of the input file config: use utf8_bom[] from utf.[ch] in git_parse_source() utf8-bom: introduce skip_utf8_bom() helper add_excludes_from_file: clarify the bom skipping logic dir: allow a BOM at the beginning of exclude files