Merge branch 'jc/maint-1.6.0-blank-at-eof' (early part) into jc/maint-blank-at-eof

Merge branch 'jc/maint-1.6.0-blank-at-eof' (early part) into jc/maint-blank-at-eof

* 'jc/maint-1.6.0-blank-at-eof' (early part):
  diff --whitespace: fix blank lines at end
  core.whitespace: split trailing-space into blank-at-{eol,eof}
  diff --color: color blank-at-eof
  diff --whitespace=warn/error: fix blank-at-eof check
  diff --whitespace=warn/error: obey blank-at-eof
  diff.c: the builtin_diff() deals with only two-file comparison
  apply --whitespace: warn blank but not necessarily empty lines at EOF
  apply --whitespace=warn/error: diagnose blank at EOF
  apply.c: split check_whitespace() into two
  apply --whitespace=fix: detect new blank lines at eof correctly
  apply --whitespace=fix: fix handling of blank lines at the eof