The ProductManifold class generalizes RigidBodyMotion, and can do
everything that the RigidBodyMotion class can.  Therefore there is
no point in keeping RigidBodyMotion any longer.  Having two
implementations for the same thing will just confuse people.

... by LagrangeLocalFiniteElementCache.

There is really no point in having this method.  Before it is called,
localgeodesicfefunctiontest already checks whether the derivative
is correct (by comparing with an FD approximation).  If a derivative
passes this test it MUST be tangential.  No need to check that
explicitly.

[cleanup] Move the FD approximation of the GFE function gradient from the GFE function into the test

It is a part of the test harness, and should not clutter the implementation of the
GFE functions themselves.

[[Imported from SVN: r9573]]

[[Imported from SVN: r8182]]

[[Imported from SVN: r8150]]

[[Imported from SVN: r8109]]

[[Imported from SVN: r8050]]

This is needed to test quad elements and higher-order gfe.

[[Imported from SVN: r8047]]

and hand it to all tests, rather than having each test create
its own.

[[Imported from SVN: r8046]]

[[Imported from SVN: r8044]]

[[Imported from SVN: r8043]]

[[Imported from SVN: r8042]]

[[Imported from SVN: r8007]]

[[Imported from SVN: r8001]]

[[Imported from SVN: r8000]]

[[Imported from SVN: r7998]]

[[Imported from SVN: r7411]]

[[Imported from SVN: r7347]]

[[Imported from SVN: r7310]]

[[Imported from SVN: r7302]]

[[Imported from SVN: r7301]]

[[Imported from SVN: r7141]]

[[Imported from SVN: r7140]]

[[Imported from SVN: r7138]]

[[Imported from SVN: r7137]]

[[Imported from SVN: r7120]]

[[Imported from SVN: r7119]]

[[Imported from SVN: r7118]]

[[Imported from SVN: r7115]]

[[Imported from SVN: r7104]]

[[Imported from SVN: r7103]]

[[Imported from SVN: r7102]]

[[Imported from SVN: r7101]]