Fix sparse warnings

Make some functions static and convert func() function prototypes to to
func(void).  Fix declaration after statement, missing declaration and
redundant declaration warnings.

Signed-off-by: Timo Hirvonen <tihirvon@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

path.c

@@ -131,7 +131,7 @@ int validate_symref(const char *path)
 	return -1;
 }
 
-static char *current_dir()
+static char *current_dir(void)
 {
 	return getcwd(pathname, sizeof(pathname));
 }