Merge branch 'martinal/topic-use-dolfin-variable-id-as-ufl-coefficient-count'
Merge branch 'johanhake/topic-set_diagonal'
Merge branch 'blechta/fix-issue-280'
Merge branch 'blechta/fix-reset-sparsity-criterion'
Fix Issue 274.
Merge branch 'garth/fix-issue-274' into next