Improve svg rendering of 1D and 2D mesh for ipython notebook.
Merge branch 'chris/xdmf-multiple-h5'
Merge branch 'garth/fix-64-bit-issues'
Add commented out code for using new ufc enabled_coefficients feature.
Some minor refactoring of SystemAssembler and prepare for using new ufc enabled_coefficients feature.
Add more outcommented use of new ufc enabled_coefficients.
Enable use of integral.enabled_coefficients() in all assemblers except
PointIntegralSolver.

bench_fem_assembly_cpp shows no performance regression.
Merge branch 'martinal/topic-add-enabled-coefficients-per-integral' into next
Merge branch 'martinal/topic-improve-mesh-svg-rendering' into next