Parallel constraint calculation on SerialMesh too

This will hopefully be a speedup for everybody, but more importantly
it should fix a bug where FEMFunctionBase boundary conditions could
not be used on a SerialMesh on more than one processor.
Comment clarifying a libmesh_error()

I'm choosing to make the SerialMesh behavior less robust here in order
to catch inefficient SerialMesh usage even when that usage isn't
technically incorrect.  We might want to make the error test more
complicated and change this error to a debug-mode warning in the
future.
Only send_receive nodes when we need to

With a serialized mesh sending nodes redundantly is inefficient; with
a synchronized SerialMesh doing so is currently an error.
Adding Ryser, 2014b.
Update Cournoyer, 2014.
Allow per-subdomain SCALAR variable support
Clarify documentation comments
Assert old SCALAR dof requests are appropriate

I doubt anyone will repeat the bug I just fixed, but if they do let's
try to do a better job of catching it.
Merge branch 'sparse_scalars'

Squashed some bugfix commits and fixed some whitespace errors.

See also #341.
creating a composite quadrature class to build up integration rules for cut cells
implementing QComposite
instantiating QComposite
suppress unused warning
creating a class define the interface for cutting an element
implement cutting an element
some execution tracing statements
demarcate inside/outside meshes
5 degree minimum angle, vs. default of 20 - results in fewer triangles.
utility ElemCutter::is_inside() etc... members
no trailing whitespace