kset.h, tar.h: add missing header guard to prevent multiple inclusion

Add missing headers to prevent ill-effects from multiple inclusion.

Found by the LGTM source code analyzer.

Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

kwset.h

@@ -1,3 +1,6 @@
+#ifndef KWSET_H
+#define KWSET_H
+
 /* This file has been copied from commit e7ac713d^ in the GNU grep git
  * repository. A few small changes have been made to adapt the code to
  * Git.
@@ -59,3 +62,4 @@ size_t kwsexec(kwset_t, char const *, size_t, struct kwsmatch *);
 /* Deallocate the given keyword set and all its associated storage. */
 void kwsfree(kwset_t);
 
+#endif /* KWSET_H */

tar.h

@@ -1,3 +1,6 @@
+#ifndef TAR_H
+#define TAR_H
+
 #define TYPEFLAG_AUTO		'\0'
 #define TYPEFLAG_REG		'0'
 #define TYPEFLAG_LNK		'2'
@@ -23,3 +26,5 @@ struct ustar_header {
 	char devminor[8];	/* 337 */
 	char prefix[155];	/* 345 */
 };
+
+#endif /* TAR_H */