Merge quagga mainline into the google ISIS code.

Merge quagga mainline into the google ISIS code.

The steps were:

  $ git checkout google-is-is
  $ git merge quagga
  $ git checkout google-is-is -- isisd

  # Resolve conflicts in the following:
  lib/md5.h
  zebra/rt_netlink.c
  zebra/zebra_rib.c
  zebra/zserv.c

Note that the content in the isisd directory is left unchanged in the
merge. As a result, changes made to isisd as part of the following
commits on the quagga mainline are dropped.

  # 8ced4e82 is the merge base, e96b3121 is the current quagga master
  $ git log --oneline --reverse 8ced4e82..e96b3121 -- isisd
  5574999 isisd: fix crash on "no router isis" (BZ#536)
  8998075 isisd: raise hello rate for DIS (BZ#539)
  306ca83 isisd: include hash.h, not hash.c
  b82cdeb delete CVS keywords
  2f65867 isisd: indent longopts array
  b511468 quagga: option "-z" ("--socket <path>") added
  05e54ee build: delete .cvsignore files
  b4e45f6 fix zebra protocol after MP-BGP changes
  7fd6cd8 isisd: fix circuit state machine
  907fd95 isisd: send proper LSP after DIS election
  d034aa0 isisd: fix wrong next-hops from SPF
  c25eaff isisd: unexpected kernel routing table (BZ#544)
  e6b03b7 isisd: implement MD5 circuit authentication