divelist.c: Fix an 'implicit declaration' warning

close() should be included from unistd.h, instead of fcntl.h for
better portability.

Signed-off-by: Lubomir I. Ivanov <neolit123@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

divelist.c

@@ -10,7 +10,7 @@
  * void mark_divelist_changed(int changed)
  * int unsaved_changes()
  */
-#include <fcntl.h>
+#include <unistd.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>