[firedrake] UFL reset

Dear firedrakers, with latest Firedrake, you'll require a new UFL + FFC combo. This is merging upstream work such that we can start looking at implementing non-affine geometries. The UFL update is a reset of master, if you have a pip install of UFL, please just reinstall as before. If, however, you're maintaining a local clone of our UFL repository you'll need to do the following to update to latest master. ** Note ** The following sequence of instructions discards any local changes you have on the master branch. You'll need to move those to a new branch before carrying on. $ git checkout master $ git fetch $ git reset --hard origin/master Please do email if something goes amiss. Cheers, Lawrence