Squashed commit of the following:

commit 465dc0303fe4a756b9a0680457a28e474c546eed
Author: Gavin Simpson <ucfagls@gmail.com>
Date:   Sat Nov 22 15:41:52 2014 -0600

    linestack now handles labels arg without setting names(x); allows expressions as labels for example

commit 59564fb5e9a93b8a6b724b32ff77c18f8d183bae
Author: Gavin Simpson <ucfagls@gmail.com>
Date:   Sat Nov 22 11:44:47 2014 -0600

    fix bug in labels length conditional test

commit c9f6b8a93d4fe8bc8ec26352ebe8772263a925a8
Author: Jari Oksanen <jari.oksanen@oulu.fi>
Date:   Wed Nov 19 13:38:05 2014 +0200

    Fix reconstruction of response matrix in CA (no CCA) for tolerance.cca
    (cherry picked from commit 0434ac4e653aeccb9b3f903a30a9fdfa55f6d7ee)

commit c9817cb9bd315847db10bb257085b206e4499530
Author: Jari Oksanen <jari.oksanen@oulu.fi>
Date:   Tue Nov 18 15:04:36 2014 +0200

    More comprehensible error message when user asks biplots of CA

    There is no biplot for CA, and its results were handled by
    biplot.default that gave weird error messages. Now biplot.cca() was
    added to give an informative error message. An alternative to this
    would be to rename biplot.rda to biplot.cca: it already has an
    error message for non-rda objects, and would only handle rda.
    (cherry picked from commit 543ead1092a37e5791408bfc771d66a9f89efe28)

commit dcf2399a79043b520f76a78b4beff85fea38a758
Author: Jari Oksanen <jari.oksanen@oulu.fi>
Date:   Tue Nov 18 13:45:18 2014 +0200

    Fail informatively if support functions for CCA are used with CA

    Several cca/rda/capscale support functions only worked with
    constrained ordination, but did not check their input. This resulted
    in cryptic error messages such as

    Error in chol2inv(Q$qr, size = rank) :
      'size' argument must be a positive integer

    Now they fail with more informative error message that tells that
    the method can be used only with constrained models.
    (cherry picked from commit 4d98639b1cd10a84ed41182a6e7123b84315e441)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/vegan@2913 edb9625f-4e0d-4859-8d74-9fd3b1da38cb