head,tail: use common suffix struct. simplify help text.

function                                             old     new   delta
head_tail_suffixes                                     -      32     +32
head_main                                            415     406      -9
packed_usage                                       29252   29234     -18
tail_suffixes                                         32       -     -32
head_suffixes                                         32       -     -32
------------------------------------------------------------------------------
(add/remove: 2/2 grow/shrink: 0/2 up/down: 32/-91)            Total: -59 bytes
   text    data     bss     dec     hex filename
 890474     497    7584  898555   db5fb busybox_old
 890415     497    7584  898496   db5c0 busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/coreutils/head_tail.h b/coreutils/head_tail.h
new file mode 100644
index 0000000..df19e41
--- /dev/null
+++ b/coreutils/head_tail.h
@@ -0,0 +1,6 @@
+/*
+ * Copyright (C) 2013 Denys Vlasenko
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+extern const struct suffix_mult head_tail_suffixes[];