Added sbox6 and sbox7 diagrams.

Rev: nettle/misc/Makefile:1.2

misc/Makefile

 # Nothing here is built or distributed by default.
 
-all: serpent-sbox3.pdf serpent-sbox4.pdf serpent-sbox5.pdf
+all: serpent-sbox3.pdf serpent-sbox4.pdf serpent-sbox5.pdf \
+	serpent-sbox6.pdf serpent-sbox7.pdf
 
 %.pdf: %.dot
 	dot -Tpdf $< -o $@