And use it in the test.

This patch uses the new 'constexpr' macro.  Hence it is C++11 only.

[[Imported from SVN: r9195]]

[[Imported from SVN: r9194]]

[[Imported from SVN: r9193]]

[[Imported from SVN: r9192]]

[[Imported from SVN: r9191]]

[[Imported from SVN: r9190]]

This is a new required method for the interface of implementations of
the TargetSpace model.  We haven't needed it previously because all
spaces considered until today were embedded isometrically in a
Euclidean space.

[[Imported from SVN: r9189]]

[[Imported from SVN: r9187]]

[[Imported from SVN: r9163]]

[[Imported from SVN: r9096]]

[[Imported from SVN: r9095]]

[[Imported from SVN: r9094]]

[[Imported from SVN: r9093]]

[[Imported from SVN: r9092]]

[[Imported from SVN: r9091]]

[[Imported from SVN: r9090]]

[[Imported from SVN: r9089]]

Not tested yet.

[[Imported from SVN: r9088]]

Not tested yet.

[[Imported from SVN: r9087]]

[[Imported from SVN: r9085]]

Not tested yet.

[[Imported from SVN: r9084]]

[[Imported from SVN: r9083]]

Not tested yet.

[[Imported from SVN: r9082]]

[[Imported from SVN: r9081]]

[[Imported from SVN: r9080]]

[[Imported from SVN: r9079]]

[[Imported from SVN: r9078]]

This is just an initial commit.  It is a copy of the corresponding code for
unit vectors, with just a few names exchanged.  The actual functionality
will come in subsequent commits.

[[Imported from SVN: r9076]]

[[Imported from SVN: r9023]]

[[Imported from SVN: r8983]]

[[Imported from SVN: r8982]]

[[Imported from SVN: r8981]]

[[Imported from SVN: r8974]]

[[Imported from SVN: r8972]]

[[Imported from SVN: r8862]]

[[Imported from SVN: r8861]]

[[Imported from SVN: r8687]]

[[Imported from SVN: r8630]]

[[Imported from SVN: r8629]]

[[Imported from SVN: r8627]]