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

cache.h

@@ -967,10 +967,12 @@ void shift_tree(const unsigned char *, const unsigned char *, unsigned char *, i
  * whitespace rules.
  * used by both diff and apply
  */
-#define WS_TRAILING_SPACE	01
+#define WS_BLANK_AT_EOL         01
 #define WS_SPACE_BEFORE_TAB	02
 #define WS_INDENT_WITH_NON_TAB	04
 #define WS_CR_AT_EOL           010
+#define WS_BLANK_AT_EOF        020
+#define WS_TRAILING_SPACE      (WS_BLANK_AT_EOL|WS_BLANK_AT_EOF)
 #define WS_DEFAULT_RULE (WS_TRAILING_SPACE|WS_SPACE_BEFORE_TAB)
 extern unsigned whitespace_rule_cfg;
 extern unsigned whitespace_rule(const char *);