Spelling fixes to progdoc.

conf/cf-lex.l

conf/conf.c

filter/filter.c

lib/checksum.c

lib/ip.c

lib/xmalloc.c

nest/cli.c

nest/proto-hooks.c

nest/proto.c

nest/rt-attr.c

nest/rt-dev.c

nest/rt-table.c

proto/bgp/bgp.c

proto/rip/rip.c

sysdep/sysdep.sgml

sysdep/unix/io.c

sysdep/unix/krt.c

sysdep/unix/log.c