fix various typos in comments.
branches: 1.1.2; 1.1.4; 1.1.10; 1.1.102;Add m68k MD cpu_in_cksum.c.Based on sys/netinet/cpu_in_cksum.c but just modifiedto use traditional MD m68k/oc_cksum.s.Makes ~5% improvements of ttcp(1) xfer rates on ATARI TT030 + SMC_TT.