GitLab

We should not return references to members of possible xvalues.
Handle is lightweight enough that copying is not a problem.

Currently, the following API-usage is straight-forward and clean but
unfortunately wrong and dangerous:

`for (const auto heh: mesh.face(fh).halfedges()) { ... }`

This is because the temporary `Face` returned by `face()` reaches the
end of its lifetime, but `halfedges()` returned a reference to a vector that
lives inside that object. Reference lifetime extension does not apply
here.

This change splits behaviour so that in rvalue context (such as
temporaries), we move out the vector instead of returning a reference to
it.

git-svn-id: http://www.openvolumemesh.org/svnrepo/OpenVolumeMesh/trunk@223 66977474-1d4b-4f09-8fe9-267525286df2

git-svn-id: http://www.openvolumemesh.org/svnrepo/OpenVolumeMesh/trunk@179 66977474-1d4b-4f09-8fe9-267525286df2

git-svn-id: http://www.openvolumemesh.org/svnrepo/OpenVolumeMesh/trunk@93 66977474-1d4b-4f09-8fe9-267525286df2

git-svn-id: http://www.openvolumemesh.org/svnrepo/OpenVolumeMesh/trunk@78 66977474-1d4b-4f09-8fe9-267525286df2

git-svn-id: http://www.openvolumemesh.org/svnrepo/OpenVolumeMesh/trunk@9 66977474-1d4b-4f09-8fe9-267525286df2