Merge with euro_ix branch v0.99.18ex17.

Update version to: 0.99.18ex18p

Of particular note:

  * includes support for GTSM:

      neighbor ... ttl-security hops X
      no neighbor ... ttl-security hops X

    where X is 1-254.  For usual case of immediately connected
    peer, X == 1.

    Cannot set ttl-security while ebgp-multihop is set, and
    vice-versa.

    If underlying O/S does not support GTSM, then will set ttl
    as per ebgp-multihop.

    In passing, have fixed various bugs in the main Quagga branch.

  * initial support for draft-ietf-idr-optional-transitive

    Does not yet support "neighbor-complete" flag.

  * main Quagga now uses TCP_CORK and permanent non-blocking

    Do not beleive TCP_CORK to be necessary for euro_ix code...
    which has a different buffering strategy.

    The euro_ix code already runs sockets permanently non-blocking.

  * various fixes to attribute intern/unintern

    Trying to remove memory leaks.  Nobody seems convinced that
    this has been perfected, yet.

  * fixes for ospfd and ospf6d issues.

Up to date with master branch up to:

  commit 538cb284864c17de66152a5236db4cd80e3e7639
  Merge: 036a6e6 8ced4e8
  Author: Paul Jakma <paul@quagga.net>
  Date:   Fri Jul 29 18:21:50 2011 +0100